I know the example of the "Holy Trinity" is often brought up by RC apologists, but this is apples and oranges (comparing this example to the more controversial teachings of the RCC which are typically defended under the banner of "development.")
While it is true that the "symbol of faith" is a development, it is not a conceptual one. What is developed, is the language used to clearly differentiate the true, Churchly understanding of God, from that which was an innovation. You have to understand, it was not as if Nicea decided between two Christologies - for as the Orthodox Fathers at Nicea knew, that of the Arians was new, not simply "another theory" of significant pedigree that they (the "Trinitarians") had to contend with.
While this may sound offensive, I honestly believe the p.o.v. which views what happened at Nicea (or the other Ecumenical Councils for that matter) in terms of "deciding between two scientific propositions" to be a graceless one. It's almost as if one doesn't believe the Church from it's infancy has known Who it's Lord is. The truth, and it's an experiential (as well as dogmatic) one, is that God has always been known by His Saints via "theoria" (spiritual vision of God - what Christ promised to the "pure of heart"), and as such, has always been known to be "one in three, and three in one". If anything has developed in this regard, it is not that experience of Pentecost itself (which has never ceased, unto the present day, in Christ's Church), but the language to express that illumined experience (in particular, to convey the experience of genuine Prophets of the New Testament, to those (like myself) who are less experienced, or do not have this quality of direct knowledge.
All genuinely Christian beliefs and practice, are born out of the same continued experience, born in the same faith. The explanations have developed to be sure, but not the substance. In fact, such a substantial development is the stuff of heresy.
Thus, while God as Trinity is part of the continued witness/experience of the Church from Her birth, can the same be said of "papal infallibility", "universal juristiction of the Pope", "indulgences" or any of the other peculiarities which make Catholicism distinct from Orthodoxy? The answer to this, I submit, is obvious - they were not part of the ancient "Western" Christian experience, let alone that of the Church in all lands, the "world wide Catholic Church" which St.Polycarp speaks of.