The Joker is a specialized predator who thrives inside his very specific ecosystem niche and would be absolutely brutalized outside of it. He might do okay in Metropolis maybe because Superman is fairly similar to Batman, but I don’t care what DC comics says, if he were to tangle with Flash? The Lanterns? Diana, aka “When I deal with my rogues, I deal with them”? Utterly pasted, clown-makeup smear on the pavement at 100 mph
And don’t get me started on how poorly he’d deal with ANY of the Avengers, Spidey and Iron Man are both funnier than he is and the X-Men would just be like “oh this is a refreshing break from trips to hell and space zombies” and bring a picnic to their beat-up-the-clown fest
He might do okay against Reed Richards since his whole thing is about the dangers of obsession but the moment he crossed Ben, Johnny, Sue, or—god help him—Victor von Fucking Doom, he’d end up in the hospital for life
… Captain America would deck him.
He might actually do okay against Captain America, but only Steve, because Steve has a number of thematic and ethical parallels to Batman that would allow Joker to actually meaningfully oppose him. Bucky or Sam, on the other hand, would put a bullet in his kneecap and call it a day.
Spider-Man has a strict No Kill Rule too, but he could call anyone and Joker would die via overprotective older heroes who knew him as a teen just starting out.
It wouldn’t even get to the kill rule point, Joker needs a dour and serious opposition force in order to thrive and him fighting Spider-Man would play out like his fight against Terry McGinnis in Batman Beyond where he just gets verbally roasted for four straight hours and starts crying because the spider-child in the rainbow onesie is being mean to him
Alongside the fact that Spider-Man doesn't Need to kill, most of the time? The Joker is strong, sure, but he doesn't have super powers. Nobody without powers breaks out of Spidey's webbing. He might dodge the first few times, but Peter only has to get him with one shot before he can tie him up and having him waiting for the cops