Since "natural law" is created and then imposed on creation by other creatures, its results vary-Aquinas might have a problem with contraception but I don't think Aristotle did. Nor do I think that the logoi mandate Aquinas' conclusion.
The ascetic approach to the spiritual life of a married couple as endorsed by monastics often leads to a marriage like St. John of Kronstadt and his wife. Not a role model for family life.
There is no imposition on creation in suggesting that sex has a purpose. It seems that this is the consistent view of the scriptures and the Fathers. All Natural Law theory says is that anyone can know the intended purpose of sex, even non-Christians. Hence, no one is without guilt if they engage in acts of sexual perversion. Certainly God reveals himself both in the scriptures, and in creation, as St. Paul teaches in Romans.
As for what Aristotle would think about contraception, it is difficult to say. He did not have a full-blown Natural Law theory of ethics. Though, if his function argument, about the nature of human person is any indication of how he approaches ethics, then it is likely that he would have rejected contraception.
A couple final points. First You seem to think that Thomistic and Aristotelian metaphysics puts essence before persons, but it is quite the opposite. Aristotle was a very vocal and, at times, harsh critic of platonism. For Aristotle, universals do NOT have independent substantial existence in some fantastical world of ideas. Individuals are the only truly substantial things. The forms only existent in particulars, and in a particular way. It is only in the mind, as abstracted from the particulars, that forms possess any kind of universal nature. And this is because this active intellect actualize the potential universal nature of such forms.
I realize that you disagree with Aristotelian metaphysics and epistemology, and I certainly have no problem with that. There are multiple approaches to philosophy, and no one of them exhausts reality. I think that thinkers like kierkegaard, phenomenologists, and personalists certainly make important contributions to the field that are easily over looked by scholastic philosophy. That all being said, I think that it is best that you don't misrepresent the view with which you disagree. I'm sure as an honest scholar, you don't want to make that mistake.
First, if you think we have swallowed Aristotelianism in its totality, and that is simply not the case. A great deal of what Aristotle thought was evident is simply incompatible with Christianity. He thought that he could prove that the universe was eternal. He didn't realize that there was such a thing as creation and contingent being. He thought that there were up to 55 Prime Movers. He even thought friendship with God was impossible. All of this is incompatible with Christianity. So we are not Aristotelians; however, just as the Fathers picked and choosed which parts of Plato's work was compatible with Christianity, so too did Aquinas pick those aspects of Aristotle that could reconciled with the faith.