On his own? Just that, and shooting. But he's never on his own. Joker's weird because it's like having a Pokemon Trainer whose moveset consists mostly of throwing Pokeballs and potions and riding a bike, and sometimes a Charizard spawns behind him and makes those attacks stronger.
Joker fighting on his own most of the time, and the entire concept of a Rebellion Gauge, is made up for the sake of the playstyle. It's completely contrary to how you fight in Persona, even if they wanted to keep his moveset restricted to just Arsene.
Which would likely apply to Persona as a whole, and despite this, we got games like Persona 4 Arena.
So the idea of the Smash team filling a ton of blanks with an original moveset isn't really too strange.
I'll give you a point for the Rebellion Gauge, but they've never been fully accurate about gauges.
- Mac's Power Meter
decreases when getting hit in Super Punch-Out, yet in Smash, it's the
fastest way to fill it.
- Durability never refills in Fire Emblem, or at least not during battle, yet it does in Smash.
- Limit Gauge can ONLY be filled by taking damage in FF7. Filling it by
dishing damage and having its own manual charging move are Smash-original.
- MP doesn't refill by doing sword attacks in Dragon Quest.
- Etc.
And by the way, all these examples are from Smash 4 and Ultimate, the two games that really
strived for accuracy.
Gauge-based gimmick are NEVER true to source material. It doesn't excuse the innaccurary, but Joker is far from the only one with that issue and at this point, it's probably intentional that they take a lot of creative liberties with gimmicks like that.
As for the Rebellion Gauge, I personally think it can be a neat representation of how Joker unlocks his Arsene Persona,
especially considering how bloody he gets. He took quite the beating, so what's the best way to summon Arsene? Make a gimmick that rewards getting pummeled.