I would have been much more open to Whitebeard having a significant growth post-GV if it wasn't for Oda etablishing that he already his broken devil fruit years before that event. Heck I was actually open to it before the flashback because we didn't know if he already had it.
-Supreme graded Nagitana
-The Gura (with years of experience confirmed)
-ACoC
All he had to do was atleast drop his supreme blade, that way we could atleast say he is just a touch away from the final product on paper, since Gura + ACoC is like 90%+ of the way there. The Supreme blade was the nail in the coffin, Oda wasn't even willing to compromise that. Oda went out of his way to make sure WB had every one of his key tools. There's not much room for growth for WB now... he's getting marginally stronger, he's gonna gain some more life experience and grow wiser, that's pretty much it.