Points 1 & 2 are somewhat in conflict: it's almost certain that 30% is artificially high but since there is a significant value for a well-supported, widely trusted payment system it's likely that they'd still see significant revenues. Most of the competition would be Amazon or Square, not app developers setting up their own credit card processor.

Competition would simply force them to actually deliver value to developers & users as well as allowing for business models with Apple's service isn't structured allow.