In particular the above title refers mostly to the Seleukids and Ptolemies. Having campaiged many times with both factions I am of the opinion that they need to be made more difficult.
In reality the Seleukids lost their empire to the Parthians, because they could never leave Syria -except Antiikhos VII- because they were too busy fighting each other. Plus there's the Hasmoneans.
Again the Ptolemies in fighting and native revolts crippled the state.
None of these major challenges ever need be faced by the player. I have to try hard to loose regions to the Parthians to get a challenge. Plus I promote the growth of the Roman Republic hoping that they will arrive to present a challenge.