How about giving them a damage cap, like electric shuttles have?
Right, I was thinking of that too (think I even said it... anyway).
So yea, I can see why there's conflicting feedback here: some players are primarily single-player, some are speaking from MP experience.
Well, we can add some form or another of mechanic that makes the martyr not unlimited-aoe. Frankly in my experience a ship that can hit an infinite number of targets for some flat amount of damage is not only inherently unbalanced, but inherently impossible to balance unless the game has pretty strict "how many units can fit on the head of a pin?" rules. AIW most definitively does not have strict rules on that point
Anyway, yea, the potential for asymptotically high total damage output is kind of a bad thing. So we can do something like the electric shuttle but let it hit everything (just with attenuated damage).
On the other hand, back to the MP question: in MP the exos (including from Spirecraft-Hard) have their point-budgets multiplied by the number of players. Please refresh my memory: would the advantage provided by Spirecraft also scale upward with the number of players? Otherwise you'd be stuck with the same number of martyrs (and whatever else) that one player would have, but you'd be getting hammered by much larger exos. I as the developer would find that funny, not sure if you would