Dang massive enemy fleets in asteroid belts. I like the idea of making belt dangerous and spooky but it could use some scaling.
I'm flying pretty low end fleet with 1 capital (Prometheus mk2) and around 3+5+5 of low end cruisers, destroyers and frigates.
First belt fleet that spawned on me was 2 Radiants and 3+5+6 of the rest (but luckily for me it prob bugged out, because after they opened the comms there was an option to just leave)
Second - 3 Guardians and load of derelicts, which didn't even matter, because they just fielded all 3 Guardians and ate me alive.
Neither of these fleets are beatable at that point. Could scale them against players fleet's DP? And/or keep them massive, but at least make them use slow ships, so you could attempt to disengage with smaller fleet.