The very problem of possible fleets size in FS and later in mods comes from the fact, that real power of GTA, PVN and later also GTVA was never truly measured. Considering the size of the most powerful navy of modern world - the US Navy, the GTVA would be capable of building hundreds if not thousands of cruisers, and possibly dozens of destroyers.
Why battles in FS are so small? Technical limitations of 1998 and 1999 and gameplay reasons.
The Sol system, including all the raw mineral supplies in Kupier Belt, Oorta Cloud and moons of gas gians has virtually unlimited resources by itself. And GTVA has about 25 of such worlds. GTA has probably something like half of this, just like PVN. Neo-Terran Front with their 3 system is several times larger then any state that ever existed on earth.
So any potential problems with insufficient mineral resources are effectively pointless, like portrayed in Sol: A History. The backstory of Prometheus in the times of FS2 is also straightforward stupid. Even rare, heavy elements which are abundant on Earth are everywhere in space, just because they sunk in young, hot and molten Earth. Such scenario is impossible in asteroid fields. I suspect that market of raw mineral resources will completely collapse on real-life Earth, when we start asteroid mining. Even gold and diamonds will become worth less then toilet paper.
Those factors probably deceived many modmakers into thinking, that GTVA is nothing more then 15 destroyers, 50 corvettes and 300 cruisers. GTVA can easily go three times the size of this and more. GTVA is effectively interstellar superpower.
So it's not that fleets in Exile are enormous, but custom fleets in many mods are ridiculously small
. Inferno actually does good work, with EA and their countless destroyers. UEF is also not bad considering the fact, that Narayana frigates are actually almost as big as Orions.
...and the Shivans? 80 juggernauts seems to be enormous for us, but even loosing it was just regular, ordinary thursday for them. They probably never even noticed. The inactive juggs that didn't jump out were probably just expendable.