In case you're too lazy to know this: Zuko actually doesn't commit warcrimes. It's not hard to know why: he doesn't perpetually act with callous disregard for any one else's lives, and it isn't hard to tell the difference.
-He doesn't engage in false-flag ops.
-He establishes a militant enemy presence every single time he starts shit in a populated area.
-He never fakes surrendering to launch an attack.
-He not once, ever, enslaves people.
He's definitely not blameless, and obviously commits crimes a bunch. Especially as the Blue Spirit. But he's not pillaging civilian goods for military purposes: he's using it for his own personal comfort, which is regular old theft. Legitimately the only thing you can argue that gets the "war" prefix is as the Blue Spirit when he takes Aang as a hostage/human shield. But probably only the last one since that has a whole ado with force alignment and prisoner custodianship that wasn't apparent or possibly true in the moment. But even without these specific classification caveat any viewer is supposed to see Azula is more callous, ruthless, vindictive, dangerous and overall worse villain than Zuko.
TL;DR Zuko isn't a self-avowed monster being portrayed as a monster.