Which of course undoubtly all of those games were inspired by the simpsons arcade game which was a beat em up and 4 player co-op
There were many, many, many incredibly influential beat em ups besides Simpsons. Many of which had 4 or even 8 players (X-Men). Phantom Breaker is specifically a homage to Guardian Heroes. I'm not sure how Scott Pilgrim works, but I could probably trace the influences if I knew more about it.
Beat em ups you should play if you want to make one (also make sure you look up move lists and whatnot, King of Dragon's and Knights of The Round are unplayable if you don't know how to parry):
King of Dragon's
Dungeons and Dragons Tower of Doom
Dungeons and Dragons Shadow over Mystara
Armoured Warriors
Golden Axe*
Streets of Rage (particularly 1 and 2)
Sengoku 3
Alien Vs Predator
Denjin Makai 2
Final Fight*
X-Men*
Battle Circuit
The Punisher
Cadillac and Dinosaurs
Dungeon Magic
Guardian Heroes
Knights of The Round
There are others too that are worth checking out (Sonic Blast Man 2 on Super Nes, Ninja Baseball Batman, etc.) but these are
essential. Especially Alien Vs Predator and Armored Warriors, which are the pinnacle of the genre imo. You don't have to like them all, but if you don't understand why other people like them, than you don't have enough understanding of the genre to make one.
Also make sure you play them on one credit though. Arcade games aren't meant for multiple credits except as practice. The score counter represents your mastery/completion rate of the game, which is reset on game over. So you didn't really beat the game if you do it on more than one coin.
red denoted = god tier
* denoted = I personally feel these haven't aged well, but they're incredibly influential so they're worth checking out.