It just seems really weird that it would be considered a stalemate when I've captured and am in the process of eating literally over 99% of their planetary population, and the last <1% are spared because of game mechanics.
I mean, sure, they captured a ton of mostly empty star systems, but pretty much now their entire civilization is what remains of their space navy.
From a real-world perspective if peace agreements were binding, Status Quo was an awful deal, and an early surrender far better: I've given up those territories up immediately-- they want three mostly empty systems back, fine. They want two more systems adjacent to what they lost... Eh... One has a wrecked megastructure in it which hurts to give up, but... THEY'RE WRECKING OUR HOME PLANET (and manufacturing base) and promising to go away if we give them 10% of the empty space we technically own. Yes, we have to give up the empty space we captured, but that involved practically no losses, as opposed to leaving our pops to be thrown into a meat grinder.
Update:
Okay, here's the results of a different battle-- This time, I attacked a federation I vastly outpowered, and my battles represented that: I swept across all of one civ's holdings-- 38 systems, five planets. I did not lose a single ship or army unit to them (I did lose a few to a trader faction I decided to punch in the face since it was on the way.). At no time did I lose any territory, or even ceded any territory back to them. I had to eventually Status Quo it because the federation-mate was across a wormhole and I didn't have the tech for it, but even by then, it was 95-100. I suffered no losses, destroyed an entire civilization, and that gave me a 5% lead?