Keeping Ronaldo makes more sense tbh. Like someone here said, Dybala is tricky to fit into certain formations like 433. He's not a winger. You could slot him in the middle of a 4231 but who plays on the left without ronaldo there? Chiesa? I'd rather he played in his natural position on the right. Don't trust kulu on the other side either. Also it would be pretty pointless signing pogba/SMS because both of them don't play well lying deep. They thrive closer to goal.
Essentially what I'm trying to say is that by catering to Dybala and making him the centre of the project with a formation that suits him, it exposes more problems elsewhere in the squad. With Dybala gone we can fund one of Pogba/SMS this year and both would thrive in a 433 with Locatelli as regista. Cr7-Vlahovic-Chiesa up front and boom there you have it.