While I would personally preferred the Flashback episode not to be finale due to my hatred of the "Out of Order" Style of Story after Man of Steel and Acolyte, I can see why for Agatha's Personal Story they did it and it's somehow works.
So After watching this Finale, I have this out of nowhere theory that Wanda some based Billy's Soul on Nicky's Soul and the New Billy is a combo of both William's and Billy/Nicky's Soul, it would explain why the boys are so similar to each other.
The Death vs Agatha/Billy fight was so much better then the Agatha vs Wanda fight in Wandavison as this show actually set up the fight throughout the Season unlike the prior fight which comes out of nowhere and didn't fits the Wandavision Style.
The Witches Road song being a Nicholas thing actually does make sense that Agatha would based the Road on something that her and Nicky would sing.
Also, Does anything think that Tommy's Soul is somewhere near Westview/Eastview? Like I don't think that it's at NorthView/Southview but he's probably at one of the real places in New Jersey.