I haven't really seen any clear evidence that Watkins is much bigger than Ayanna, though she is regularly listed as being 1 inch taller. In that freshman year, when Ayanna arrived at Storrs already a bit of a body builder, she looked bigger than she does now, so perhaps it will turn out to be visually obvious when we play SC this season. At least, she looks more slender in these videos than I remember from three seasons ago when she outmuscled Monika Czinano in the Iowa game. Maybe a way to think about is to compare both Ayanna and Watkins to Aaliyah, who I think is bigger than the two of them. Ayanna as a freshman seemed to be as strong as Aaliyah, who is very strong.
But all that being said, I agree with your overall assessment. I suspect Watkins will come back already more developed in her skills than Ayanna. And just for context, Saniya Feagin had better offensive skills and comparable defensive skills to Watkins and went in the 2nd round of the draft, which is where I'd expect Watkins to go, if she returns to form. Ayanna still has a ways to go to make it to the draft -- returning to her freshman year form isn't likely to be enough. And that is entirely up to her and whatever competitive fire she brings this season. I'm optimistic.
And just to finish an earlier thought, Aaliyah went in the first round of the draft because she was much more skillful on both ends of the floor than Feagin or Watkins and certainly more so than Ayanna three season ago.