I remember this one AMAZING game i had, as lusitanni, where everyone balanced out everyone else. No superpowers emerged. AND no intervention from me, aside from what lusitanni would usually do. And, that was after a lot of years too.

Seleucia and ptolemies had fought to a standstill. ptolemies had lost the whole syrian coast to seleukids, but kept the whole egypt. however seleucia was crippled, cuz in the east bactrians and pahlavans had divided the kingdom pretty much half/half, as far as just south of the caspian sea i believe. as for asia minor, pontus took it, then lost to KH (who had taken the whole continental Greece, but were at peace with epirus who was confining them to greece), who then lost it to the Lesbo makedonian empire. The hai were warring up north, fighting against sauromatae and their "protectors", the (KH) bosphoran kingdom.
The aedui won the civil war and were quite dominant for a bit, but then they invaded iberia and lost a lot of troops doing that. after that, sweboz had the northeast, romans the southeast and me the southwest, aedui confined in the northwest. Romans had good drives, but always had a major thorn in their side. Carthage was actually winning the war down south. then i attacked carthage, and romans retook the south (and sicilia), but then epiros sent this one army that cut a large swath into roman territories, and i challenged them in Gaul (took the southwest from 'em). they just couldn't catch a break.

Just to say, changes dont have to be drastic. it's already possible to have that awesome game OP was talking about. Just extremely rare. a little tweaking and the new engine hopefully will make it happen more often.