A deleted scene from Avengers: Infinity War shows Marvel’s original plan for Bruce Banner’s transformation into Professor Hulk. In it, we were supposed to witness Bruce Banner defeat Cull Obsidian himself while he’s in the Hulkbuster armor after Hulk refuses to emerge. The fallout of this interaction was to have Professor Hulk emerge from the Wakandan jungle and encounter Black Widow and Falcon, with Natasha attempting to calm the Hulk down as she did in Avengers: Age of Ultron, only to discover that Bruce Banner and the Hulk are no longer separate personalities.
The decision to remove Professor Hulk from Infinity War and delay his introduction until Avengers: Endgame came during production, as Bruce Banner’s scenes in Infinity War were reshot. The writers of Infinity War have attributed the removal of Professor Hulk party to timing, as they explained that it would have felt too tonally inconsistent to have Bruce have this high moment of triumph over the Hulk while everyone else was approaching their lowest point of failure.
Personally, I can understand where the filmmakers are coming from, but I would have much preferred for this scene to be in the final product. To me, it’s very apparent that the moments with the Hulk refusing to fight for Bruce were meant to pay off with this scene of the two combining into one, and I would have appreciated a brief moment of victory before the worst defeat the Avengers have ever faced.