I think an Trystane who isn't Aegon but who does pretty much everything Aegon does fits a little bit better, just because it's a bit less backstory to explain. It would just be that Doran was a co-conspirator with Varys and Illyrio (I think it was intentional that Varys mentioned multiple colleagues last episode) and once they got word that Viserys and Drogo were dead, the plan shifted away from them and towards Dany, who they planned to tie down with a marriage to Trystane. When Trystane finds out he's going to marry Dany when she arrives, he decides he should start conquering now to impress her when she gets here, and attacks Storm's End, just like Aegon. He basically becomes a weird fusion of Aegon, Quentyn, and Arianne all in one.