Come on now fam lol, the source material is cool but you have to kinda streamline of that stuff for film. This is akin to people up in arms about Ms Marvel not being an inhuman like it's not going to be a nightmare to explain the distinction to casuals.
We don't need Joe Fixit to reach a point where there's a merger. And as for Hulk in Ragnarok, I wouldn't call it a different personality all together.
Savage Hulk is a like a giant mindless baby. Him staying transformed on Sakarr for 2 years straight brought that same Hulk into what I would call more like a toddler phase. He could speak in short coherant sentences because he had been "out" long enough to learn and grown a bit mentally.
In fact, I'd say Banner doesn't reach that merger without Hulk gaining the capacity to understand shyt like, aye you can't be running around smashing shyt with reckless abandon, people will fear and hate you. The more self aware, toddler-esque Hulk understands enough to know that it's in his best interest to share the light with Banner as long as he doesn't have to sit in the background dormant.
But that cannot hold. Only other incarnation I really want to see on film is Maestro, which I think there is a perfectly logical lane for. He's going to have to bush this 'smart Hulk" transformation if he's going back to Sakarr at some point. And if/when he comes back to earth, he's going have to try and improve upon the merger without sacrificing so much raw power just to keep his wits about him.