Classical Theism

I am working through Fesers book Neo-Scholastic Essays and in chapter 7, he distinguishes the metaphysical assumptions made between the fifth way and the ID-style design arguments; the fifth way assumes that teleology is intrinsic, whereas the ID-style arguments assume that teleology is extrinsic. He then concludes (if I am understanding him correctly) that the consistent thomist would reject the ID-style arguments on the grounds that it assumes an incorrect view of teleology; however, I am inclined to think this is false. Take the following argument:

P1 The bacterial flagellum exists
P2 The probability the bacterial flagellum existing is more likely on theism rather than atheism
C Therefore, God exists

This doesn't seem to me to entail that biological organsims can't have intrinsic teleology, but I may be wrong. I think the mantra of "irreducible-complexity" may be the source of Feser's objection. I think if the claim ID-theorists make was that some natural phenomena can only be explained by theism (is literally irreducibly-complex), than perhaps Feser may have a point, but I am not even really sure if that stands in contradiction with the notion of finality.

I suppose the question I am trying to have answered is: Does finality falsify ID-style theistic arguments? Why or why not?