Which makes them suck even worse against the fires you do start on board their ship. Many smaller boarding parties are just free crew training anyway. There's also the "shield room damage thing" that the AI tends to prioritize. Not sure if it's just shield room boarders that they'll swarm against, or if fires count too. I'm sure I've seen them all jump into the shield room oven-bake though, cancelling the boarding attempt asap. Fires+laser damage clears mantis very quickly when they all squeeze into a size four shield room.
There's plenty of ships that it isn't too hard to toast both piloting and shields with the beam (or any combination with the weapon room), that turns many encounters into an easy wait-out.
Still, gotta get those shields down, but with the beam charge being what it is, that's not a huge problem. You'll usually get 1-2 volleys in and then start a few blazes. It's just a prettier and more damaging anti-bio beam of sorts. Kind of. I like it anyway. It's not a halberd or glaive, but it's probably more fun.
It's also nice to have a change with beams, that instead of trying to find "magic pixels" that give you an extra room hit, you're trying for max squares hit, but useful ones. Even systemless rooms are fine if you can hit three squares between piloting and shields. There's a lot of judgement calls for its most effective uses, depending on enemy and your own setup. But the fact is, it'll look devastatingly evil eventually (except vs AIs and lanius).
edit: I'm wrong about the normal damage against crews. I think (maybe. There does seem to be varying damage for lasers vs crew, so maybe it does have 1 10pt crew damage tick on it). Just lots of eventual fire damage. The normal damage to rooms was meant to mean from the fires. It eventually ticks up.