What's the point of them? If we're just assuming you have a gang, and they do what you say most of the time, and anyone can have a gang like this, why even have special Moves for "imposing your will" or "having your gang fight for you"? Why not just use basic moves or custom moves for those situations like we'd do with the Maestro D'?
Leadership can be used
in absentia for starters. I can have my Hardholder order a part of his gang down the mountains to Terminal City to go raiding, and if I make my Leadership roll I've got one or more holds that can help them fight even when I'm not there. The risk in that at-a-distance scenario is that they surrender to the bandits, offer them inside info on my holding in exchange for mercy, and then bugger off into the wilderness.
If I don't have Leadership, then I can't even do that mechanical stuff to start with. Then I'm just telling a gang what to do in-fiction and reaping/suffering consequences that result from the ficiton, possibly with some basic moves to help the reaping/suffering along.
So, Leadership exists because it's interesting. It lets me do things directly to the fiction, as a player, that I wouldn't have direct access to normally. Without it I have to use more general mechanical tools to cobble together that kind of fiction if I really want to go there (with all the attendant messiness and MC-infused interestingness when I miss even one of those many basic moves).
Pack Alpha opens up similar fictional horizons. It's less used for telling a gang what to do, and more for putting down mutinies. The fictional horizon it opens up is a focused mutiny/crushing mutiny scene. That kind of scene is eventually integral to playing a Chopper, so it makes sense to support it mechanically. Without Pack Alpha you can get into that kind of scene, but it's going to be more fictionally piecemeal, take more play to set up and resolve, and be the kind of deal that will likely come up once and then irrevocably alter the relationship to the gang for the Pack-Alpha-less character.
I mean, think about the likely fictional circumstances. You've got a dozen violent individuals who have decided that you're done telling them what to do. They revolt. Most ways of imposing your will without the Pack Alpha move aren't going to be clean, repercussion-free actions. If you're clever and lucky you'll get the gang to do what you want, but unless you're exceptionally clever and lucky there will be piles of Badness that the MC will have inserted. The gang will never be the same again, and likely the crushed mutiny will come back to haunt you. If you're not clever or lucky enough, you've got a dozen violent individuals who are not only done with you as leader, but now you've pissed them off and you're probably under concentrated fire. Have fun!
Not so with Pack Alpha. You make the roll 10+? You're free and clear. Move along!
So, mechanically, Pack Alpha supports the archetype of the Chopper well: you get to have disputes with your gang, and you get to be a hard-ass who puts them in their place every once in a while. Rather than being a big huge blow-up that is going to define this and a few sessions, it'll be one event in a larger set of circumstances for your Chopper.
Mechanically, Leadership does the same for the Hardholder. It makes being leader-ly a supported part of the archetype, so that you can get into those power struggles in a quickly-resolved way, often enough to make it just part of being a Hardholder.