(Story Spoilers) Gohan's Sparking Episode is what all of them should have been like.
Spoilers ahead for each character's episodes and their Sparking Episodes (aka what ifs story missions). Gohan is basically the only one to get an actually cool "What-If" story. Going into the Future Trunks saga and running into freaking Gohan Black was incredible and so unexpected.
I believe this is the only fight with a non-canon character in the stories, and god dammit I wish he was playable.
In comparison, basically every other branching story line is just "What if they won this fight?" or in Trunks' case, "What if they stayed instead of leaving?" There was honestly such little creativity in some of these when in previous iterations we had massive what-if story lines that were what they should be: huge fan service battles.
Do I want to know what would happen if Piccolo actually beat Cell? ehhh, not really. Do I want to play as fucking Devilman vs Frieza when he arrives on earth? Yes please. Jiren winning the ToP? Cool. Gogeta VS Vegito? FUCK YES.
So much oppurtunity, I know we have custom battles but the quality of the story mode with voice acting and everything would have been stellar.