At least in the old lore, part of the Hegemony's strength was that they actually had core worlds (which in the new lore would be industrial Chicomoztoc, farming Jangala and cultural Eventide). Tri-Tachyon has Culann star forge and... that's about it, Eochu Bres isn't much of a powerhouse. The League sort-of has what the Hegemony has (industrial Kazeron, farming Mazalot and ?cultural Fikenhild) except not quite as good, plus the League bickers amongst themselves when they're not facing an external threat. The Luddics and the Sindrians are... well, they're the Luddics and the Sindrians.
So I don't find it weird that the Hegemony loses less than others. I also think they've lost plenty: Askonia is a definite backfire for the Hegemony, Mayasura was a tactical win but their goal was to glass Mairaath so it can't be used against them which wasn't (entirely) successful (presumably due to Persean intervention), making it a strategic loss; Naraka and even Aztlan were hit in the AI Wars (with on-going consequences), and some of the devastated systems (Tia-Ta'xet, Yma-Warawara) could well be Hegemony-controlled systems beforehand.