Firstly, the fight against Eternatus didn't properly establish a threat for me. Leon attacks it once and uses a regular Pokeball of all things to try and capture Eternatus. It then takes one more hit from Leon, who then gets taken out for his efforts, and Eternatus is then captured by the player character after two more hits. Eternatus never attacks during any of this or does much else to really feel like the threat it's supposed to be.

What should've happened is Leon should still be taken out, but doesn't just lay on the ground watching the whole fight. Have him fading in and out with brief scenes of an epic battle going on, and then leave the ending ambiguous. We never see it. Leon wakes after the fight to discover the player character won. He has no idea what they did, and it shakes him.

He sits in that locker room questioning not just himself, but the person he's about to battle. He has no idea what he's up against because he never got to actually see it. What can this kid do? How did he do it? He wonders and we, the viewer, also wonder because we saw no more than he did. We better resonate with Leon and the story barely changes, but the fight could get a bit more time by being shown in time skipped brief shots.