Yes the mummies can be quite laggy and somewhat annoying because when player's go about spawning them they don;t do so with anything that resembles self control. Thats actually always been something of an issue, like having 30 mummies surrounding the cross producing epic amounts of lag
Saying there's no RP opportunity is a vast understatement.
That Trollsbane people come together to rid there town of the mummies is actually pretty interesting, they work together in a way you don't ever see any other time of the year.
The 'standard' for some groups is this notion of standing around and talking being what is considered good RP. Or sitting around the fireplace telling stories or some other nonsense that can easily be done in a text only game. This is RP(loosely), but it's not the best RP in the world.
Rather then looking at Mas as a downside use the opportunity to take your character and do some things differently then they normally do. Use this chance to more naturally RP with the environment you are in as a consideration for your character's actions(something so many players fail to do). Create RP using the elements of Mas rather then say there's no chance to RP at all because no ones hanging out at the workshop depot etc.
IF you think MAS is bad then you would have hated the lich war''s (can we do that again please) when stepping outside meant being face smashed by superior demon skeletions that burst into an ice flame after you killed them. Good times^^