That's nonsense. Anyone can try to form a band on whatever terms they want. Moz & Marr's accounts have been that they did the work, the management, the strategizing and planning and everything else and Joyce & Rourke played and then partied.
It's like starting a company. If I formed a company with a few other people, I could set it up with all of them as equal partners, or just pick one or two others to be equal partners, and the others would be employed with the salary any partners and I would determine to be fair. If the would-be employee didn't like those terms, we'd pick someone else.
Just because it's a "band" doesn't mean they're all equals, or even meant to be.
So you think that Morrissey & Marr told Joyce up front, before they even played ONE GIG...hey we're only gonna give you 10% and he said OKAY???
Do you really think ANYBODY is that stupid?