“That such a doctrine [distinction of essence and existence] is his greatest or most important philosophical doctrine, I deny: the real distinction between essence and existence is an instance (and development) of a more general and overarching principle, namely, the real distinction between potency and act, an Aristotelian doctrine. Thus, every application of the doctrine of essence and existence is in fact an application of the doctrine of potency and act.” (from the comments on Quaeritur: Aren’t You Unfairly Criticizing Gilson?)
I think, if correct, such a statement would shows why Thomistic philosophy is properly called Aristotelian philosophy: the primary distinction between philosophers comes not from what they think can be proven from certain principles, but rather from the principles upon which those conclusions depend. (see Where Philosophers Disagree by M. Berquist) Thus, if the principle distinction St. Thomas admits is that of potency and act, he is an Aristotelian philosopher who happens to disagree or expand on one or more of the conclusions that one could draw from that principle. If, on the other hand, the distinction of essence/existence is a novel principle, we have a reason to deny that he is an Aristotelian philosopher: he disagrees with Aristotle about the principles of Metaphysics.
Regardless of which side one takes, one can coherently speak of a “Thomist” philosophy: such a philosophy would either be the philosophy that follow from a distinctly Thomistic principle, or it would be one that considers St. Thomas to be the most eminent expositor of Aristotle.