You don't actually need to kill them faster than it builds them elsewhere, you just need to be able to kill them while doing something else(even if its just building up your own army for a strike somewhere), and have better than proportional losses, but yeah, non-trivial.
And or/you need to attrit the AI in the places you want to go, while causing him to reinforce uselessly in places you have no interest in. Misdirection is definitely worthwhile!
Yeah, those are good ideas, but Nibelung's attrition seems to suggest doing the opposite: seeking out concentrations of enemy ships even if they're not somewhere you would otherwise want to go, or even if you're not doing anything else useful in the meantime.
Well, it is safe to assume that what we want, with this strategy, is to drain enemy resources slowly without suffering much losses.
That sounds like a recipe for attacking the enemy where he's strongest and ignoring the strategic importance of targets, which is contrary to most of the usual good strategies (like surgical strikes). Maybe I'm misinterpreting.
It makes sense to me to use some focused attrition tactics while playing normally, but based on how the AI gets reinforcements spread across many planets, I think that trying to win by attrition across the whole galaxy is going to get you nowhere. In a typical game, does the AI have more ships on the board at the beginning, or when you win?