This. Everyone complaining that Rome is OP - have any of you actually recreated the historic conquests on the historic timeline? It's extremely difficult, nearly impossible - I almost guarantee most people complaining haven't done it. Has the AI ever done it? Nope.
So which is the bigger problem, the country that conquered the entire Mediterranean IRL has an easy time conquering the Mediterranean, or that Rome only unites Italy 50% of the time (the case in past patches) or only really expands out of Italy to Gaul, Dacia, and Illyria (still kind of the case now).
Yeah, you played the easiest country in the game and then complained it's easy. The problem isn't Rome, it's what you want out of it.
This is completely wrong. The population is high because historically it was high - Rome was famous for it's absurd population, allowing it to swallow losses that were catastrophic for Carthage, Macedon, the Seleukids, and Mithridates. Rome is overpowered because of its population and neighbors - these cannot and will not ever change. Add to that some small military buffs, a good levy composition, and conquest-focused missions. That's it. Rome is not OP, it's arguably still not aggressive enough. Have you ever seen Rome annex Carthage - the whole thing from Tunisia to Spain, not just the city itself and surrounding countryside?
If it's buffed, it's not so the player will have an easy time. It's so the AI will have an easy time and so somewhat predictably become the threat they should become.
The successors are a lot of fun because of their particular historical position and the fact that they just got a DLC. There are plenty of regions that actually need work, most of all India. Rome is nowhere near the pariah it's being made out to be.
Now there is certainly a case to be made here for better coalitions. For tribal unions to form in response to Rome (through a Vercingetorix like figure), creating a strong state to resist expansion. However, you cannot just invent a major power in Iberia because you think it would be fun though. The countries that existed are the ones that can. Their strength is based on what it reasonably was. All PDX games follow this philosophy, creating natural inequality.