To prevent majors interfering in minor actions around the world, you could set the threshold at 25% if a major is involved, 40% if it's a minor fabricating on a minor. It wouldn't help with the China issue, but a Saudi Yemen war or a Peru versus Ecuador fight could work, at least early in the game.
edit - Sorry, the US still has guarantees on the Americas. For the Peru-Ecuador thing to work, Monroe Doctrine would probably have to be restricted to externals-only until WT gets higher.
p.s. (Neither helps historicity THAT much, since the Ecuador-Peru war happened after the world war was raging hot already, but a change like this should help with your particular problem playing no-rules multiplayer.)
Technically the Monroe Doctrine was aimed at external (non-American) nations only, but I'm not sure how this works in-game as I've never looked closely at it. I'm assuming the US just blanket-guarantees all American nations, which is a problem since historically the US only cared about European intervention, not internal American affairs.