A World Champion in professional wrestling should be outstanding at the craft or so imposing as a force of nature that they resonate as invincible. They should be worthy, in that intangible way, of holding the strap: a genius, a megastar, or an attraction.
It's professional wrestling, so they should, ideally, in most circumstances work fantastic professional wrestling matches heavy on work rate. This term is often conflated with high spots and excitement and sh*t some people have this weird thing about not liking, but it's not that.
It's about how hard the wrestler works, and it's the absolute least a wrestler can do, 99 times out of 99.1. Nobody is getting over the way Hulk Hogan got over in the 1980s WWF anymore. The world is less "colourful and simplistic morality play that muscle beast with skullet proves is conquerable" and more "agonising wave upon wave of insurmountable awfulness".
A World Champion should make the belt, and not the other way 'round. It's not a magical property that Vince McMahon believes will make a superstar because that person is large.
A World Champion in professional wrestling should not be sh*tty at literally all of these attributes...