Yeah that's pretty much the crux of it.
We could deepfake Mark Ruffalo over Ed Norton in the Incredible Hulk so that yada yada continuity, but the physical performance of Norton is not what Ruffalo would of done had he actually been in the film. The way he talks, walks, acts, moves, twitches and everything. You can put one face over the other but you cannot change the fundemental performance that would make it convincing.
I think if you used a short clip to give context within another edit as a flashback, then it would probably work. But watching the entire film with a pasted face over the top would be uncanny as you'd just see the performance of the original actor.
All I can see with this clip is Chris Pratt's performance and facial ticks. While it's a very impressive piece of work, I can't see it as one cohesive thing yet.