Possibilities (these aren't necessarily linked):
Earn XP as desired by designer. Limit XP spending by RL time.
Only be significantly concerned with higher level abilities, in Wod/CoD terms, dots 4-5 (expert) for sure, perhaps 3 (professional). Either give people more XP to buy lower level skills etc to be who they want to be at start, or let them earn and spend on these as much as they like.
Expert and above require approval.
Limit expert dots.
Give players a set number of xps. Thats where they can get to.
Remove all subjective skills, especially ones players have a hard time limiting themselves with.
Only have character change at the end of X, a year, a television/streaming season, campaign arc.
Exceptions: maybe allow some level 1 ability adds, or just limit a change of more than 1, or require any mid-season change to have a strongly (I define this strong as impactful to the character, and involving either players not in the character's immediate circle, staffer moderation, a permanantly lost cost, etc) presented scene or three.
Players lay out desired/potential character arcs, and gain changes only by that means. These arcs can change via PC or ST events, but it should happen where the story can be consumed publicly.
While many RPGs and western fiction pay a lot of attention to the fast growth phase, that phase doesn't have to extend forever. Fiction is often about change of character, not massive fast changes in skill sets. This could be done via some sort of ranking of personality traits that can change (see Pendragon virtues, Spiritual Attributes in The Riddle of Steel, all your traits in Masks, Humanity/Empathy in cyberpunk, Madness Meters in Unknown Armies, etc) but MU* players are like most RPG players and don't want to be held to a standard of IC presentation (see social skills vs writing).