Thinking about it, maybe martys don't seem so overpowered on single player, due to smaller warp gate attacks. I don't suppose you get many waves of 3000+ ships on single player (And at times 2 very close together, seeing 7k ships incoming isn't unusual with 3 players)
"Hmmmm..." indeed. That's a good point. I'm used to usually playing with 4-6 players. Depending on what settings you're using, once you're past the early parts of the game thousands of ships at a time isn't just not unusual, it's...well, very usual. A few hundred loose threat ships that might be considered a problem in single player are just background noise at that point.
The thing is, with Martyrs, the difficulty of those doesn't really scale up like it does without them. Without them, 2000 ships compared to 200 ships is a big frickin' deal in terms of what you need to stop them. If you have Martyrs handy, they're pretty much identical: park a mk1 Martyr in front of it, and the problem goes away.
They do a million damage
to every ship in an enormous range, and you get roughly 40 hojillion of them on an 80-planet map. When they're hitting hundreds or thousands of ships each, that's hundreds of millions or even billions of damage from each one. A lot of that's overkill, but still...at that point, who even cares about the tractor beams or anything? They make lots of ships very dead.
I don't use them as my only defense, but just using them for the particularly ugly situations and/or when I'm feeling lazy, I don't come close to running out, and they're good enough that I don't bother with much else other than things like the occasional implosion artillery when the situation calls for it. "Throw Martyrs at it until it goes away" is a surprisingly effective and practical solution to many problems, and it often doesn't take more than one or two.