1.) Act and potency are really divided and not just notionally distinct. We can have a skill to play music when not playing.
2.) Act and potency are not correlatives. Potency depends on act to exist but not vice versa. Shown in three ways:
a.) Potency is defined relative to act but act is not defined (Metaphysics IX. esp. c. 6)
b.) If act as such depends on potency then act, as act, is potential. But they are really distinct (see 1).
c.) Potency depends on act intrinsically and in its logos but act does not so depend on potency (see 2a)
3.) If act and potency are not correlatives and are really distinct, an-act-that-lacks-all-potency (pure act) is metaphysically and not just logically possible. In other words, when we say that pure act is “possible” we don’t just mean that we see no contradiction (and for all we know there might be one) but that we see that there is not a contradiction.*
4.) To prove that there are no contradictions in a necessary thing is to know it exists, in the same way that to prove there is no contradiction in denying the Fifth Postulate proves that Non-Euclidean quantities exist. Call this the Leibniz-Brentano Axiom.
5.) Whatever lacks all potency is by definition necessary.
6.) Pure act exists.
*When apologetics seeks to prove that there are no contradictions in the dogmas of the faith, it arguably only establishes logical possibility.