I would agree with what Alveus, LBK, and Fr. Anastasios said. As for my own 2 cents... I was under the impression that the Orthodox also believed in the divine simplicity. For example, I think the Orthodox still accept what St. John of Damascus says:
"We, therefore, both know and confess that God is without beginning, without end, eternal and everlasting, uncreate, unchangeable, invariable, simple, uncompound
..." - Exact Exposition of the Orthodox Faith, 1, 2
Regarding development of doctrine within Orthodoxy, here are two quotes from the Church Fathers which perhaps begin to articulate the Orthodox position:
But some one will say, perhaps, Shall there, then, be no progress in Christ's Church? Certainly; all possible progress. For what being is there, so envious of men, so full of hatred to God, who would seek to forbid it? Yet on condition that it be real progress, not alteration of the faith. For progress requires that the subject be enlarged n itself, alteration, that it be transformed into something else. The intelligence, then, the knowledge, the wisdom, as well of individuals as of all, as well of one man as of the whole Church, ought, in the course of ages and centuries, to increase and make much and vigorous progress; but yet only in its own kind; that is to say, in the same doctrine, in the same sense, and in the same meaning.
The growth of religion in the soul must be analogous to the growth of the body, which, though in process of years it is developed and attains its full size, yet remains still the same. There is a wide difference between the flower of youth and the maturity of age; yet they who were once young are still the same now that they have become old, insomuch that though the stature and outward form of the individual are changed, yet his nature is one and the same, his person is one and the same. An infant's limbs are small, a young man's large, yet the infant and the young man are the same. Men when full grown have the same number of joints that they had when children; and if there be any to which maturer age has given birth these were already present in embryo, so that nothing new is produced in them when old which was not already latent in them when children. This, then, is undoubtedly the true and legitimate rule of progress, this the established and most beautiful order of growth, that mature age ever develops in the man those parts and forms which the wisdom of the Creator had already framed beforehand in the infant. Whereas, if the human form were changed into some shape belonging to another kind, or at any rate, if the number of its limbs were increased or diminished, the result would be that the whole body would become either a wreck or a monster, or, at the least, would be impaired and enfeebled.
In like manner, it behooves Christian doctrine to follow the same laws of progress, so as to be consolidated by years, enlarged by time, refined by age, and yet, withal, to continue uncorrupt and unadulterate, complete and perfect in all the measurement of its parts, and, so to speak, in all its proper members and senses, admitting no change, no waste of its distinctive property, no variation in its limits.
For example: Our forefathers in the old time sowed wheat in the Church's field. It would be most unmeet and iniquitous if we, their descendants, instead of the genuine truth of grain, should reap the counterfeit error of tares. This rather should be the result—there should be no discrepancy between the first and the last. From doctrine which was sown as wheat, we should reap, in the increase, doctrine of the same kind— wheat also; so that when in process of time any of the original seed is developed, and now flourishes under cultivation, no change may ensue in the character of the plant. There may supervene shape, form, variation in outward appearance, but the nature of each kind must remain the same. God forbid that those rose-beds of Catholic interpretation should be converted into thorns and thistles. God forbid that in that spiritual paradise from plants of cinnamon and balsam, darnel and wolfsbane should of a sudden shoot forth.
Therefore, whatever has been sown by the fidelity of the Fathers in this husbandry of God's Church, the same ought to be cultivated and taken care of by the industry of their children, the same ought to flourish and ripen, the same ought to advance and go forward to perfection. For it is right that those ancient doctrines of heavenly philosophy should, as time goes on, be cared for, smoothed, polished; but not that they should be changed, not that they should be maimed, not that they should be mutilated. They may receive proof, illustration, definiteness; but they must retain withal their completeness, their integrity, their characteristic properties.
For if once this license of impious fraud be admitted, I dread to say in how great danger religion will be of being utterly destroyed and annihilated. For if any one part of Catholic truth be given up, another, and another, and another will thenceforward be given up as a matter of course, and the several individual portions having been rejected, what will follow in the end but the rejection of the whole? On the other hand, if what is new begins to be mingled with what is old, foreign with domestic, profane with sacred, the custom will of necessity creep on universally, till at last the Church will have nothing left untampered with, nothing unadulterated, nothing sound, nothing pure; but where formerly there was a sanctuary of chaste and undefiled truth, thenceforward there will be a brothel of impious and base errors. May God's mercy avert this wickedness from the minds of his servants; be it rather the frenzy of the ungodly.
But the Church of Christ, the careful and watchful guardian of the doctrines deposited in her charge, never changes anything in them, never diminishes, never adds, does not cut off what is necessary, does not add what is superfluous, does not lose her own, does not appropriate what is another's, but while dealing faithfully and judiciously with ancient doctrine, keeps this one object carefully in view—if there be anything which antiquity has left shapeless and rudimentary, to fashion and polish it, if anything already reduced to shape and developed, to consolidate and strengthen it, if any already ratified and defined, to keep and guard it. Finally, what other object have Councils ever aimed at in their decrees, than to provide that what was before believed in simplicity should in future be believed intelligently, that what was before preached coldly should in future be preached earnestly, that what was before practised negligently should thenceforward be practised with double solicitude? This, I say, is what the Catholic Church, roused by the novelties of heretics, has accomplished by the decrees of her Councils,— this, and nothing else—she has thenceforward consigned to posterity in writing what she had received from those of olden times only by tradition, comprising a great amount of matter in a few words, and often, for the better understanding, designating an old article of the faith by the characteristic of a new name. - St. Vincent of Lerins, The Commonitory, 23
To this I may compare the case of Theology except that it proceeds the reverse way. For in the case by which I have illustrated it the change is made by successive subtractions; whereas here perfection is reached by additions. For the matter stands thus. The Old Testament proclaimed the Father openly, and the Son more obscurely. The New manifested the Son, and suggested the Deity of the Spirit. Now the Spirit Himself dwells among us, and supplies us with a clearer demonstration of Himself. For it was not safe, when the Godhead of the Father was not yet acknowledged, plainly to proclaim the Son; nor when that of the Son was not yet received to burden us further (if I may use so bold an expression) with the Holy Ghost; lest perhaps people might, like men loaded with food beyond their strength, and presenting eyes as yet too weak to bear it to the sun's light, risk the loss even of that which was within the reach of their powers; but that by gradual additions, and, as David says, Goings up, and advances and progress from glory to glory, the Light of the Trinity might shine upon the more illuminated.
For this reason it was, I think, that He gradually came to dwell in the Disciples, measuring Himself out to them according to their capacity to receive Him, at the beginning of the Gospel, after the Passion, after the Ascension, making perfect their powers, being breathed upon them, and appearing in fiery tongues. And indeed it is little by little that He is declared by Jesus, as you will learn for yourself if you will read more carefully. I will ask the Father, He says, and He will send you another Comforter, even the spirit of Truth. This He said that He might not seem to be a rival God, or to make His discourses to them by another authority. Again, He shall send Him, but it is in My Name. He leaves out the I will ask, but He keeps the Shall send, then again, I will send,—His own dignity. Then shall come, the authority of the Spirit. - St. Gregory the Theologian, Oration 31, 26