This isn't official info; this is just what I think (that's one reason why I like Oddworld; there are so many different ways of looking at things):
There is more than one RuptureFarms factory, and Molluck is the head of the biggest one, just as Dripik is in charge of the largest Slig Barracks and Phleg is the head of the largest Bonewerkz.
The 'Gluk Council' at the beginning of AO is actually the CEOs of the other RuptureFarmses (or whatever the hell the plural of RuptureFarms is); and they are holding a meeting to try to find a way to save their failing business.
Molluck is important, but in no way the head of the Cartel. Maggie is the ruler of the Cartel, and below her are Glock Stars. Each one is in charge of chains of factories as a whole (only one Glock Star is in charge of RuptureFarms as a company, but each RuptureFarms factory is run by a Big Cheese (of which Molluck is one). Same for B'werkz and Barracks, etc).
Aslik is the head of Feeco Depot, but the VP of Molluck's RuptureFarms.
I've no idea why Molluck left the Brewery to someone as incompetent as the Brewmaster (I've asked Alf about it, but he has yet to reply). Maybe the incompetence is a front, or maybe the Brewmaster knows something about Molluck that Molluck doesn't want anyone else to know, and thus the Brewmaster exerts some kind of hold on Molluck.
Or maybe Molluck was drunk when he signed the contract.

On Earth, that would make it invalid, but this is Oddworld.
Maybe they're long-time friends, or the Brewmaster did Molluck a huge favour and the Brewery is his reward.
Or, most wonderful of all, maybe we'll find out in a future game.