One thing everyone needs to understand. Actually two things

1.) I am not denying Rome's (massive) impact on history, nor do I presume to deny their military prowess. Ave! They did a good job.
I am merely of the opinion that phalanx armies are superior.

2.) The most important thing one needs to understand is, as you stated in a way, Rome's victory over Macedonia was due to the fact that the Macedonians and the rest of the Greeks were tattered by so many wars among each other.

If you really want to see which faction could have been greater or is in the game, you need to pit each factions elite against the other's. It's the only way to settle this matter.

And the army posted above is not a-historical, let's get our semantics straight, it is, I will be the first to admit, anachronistic. But that is a different issue.
Now, antisocialmunky put it very well, the Macedonians that the Romans faced were no rabble, nor were they Alexander's finest.

On a sidenote (and back on topic). Maion's army is defeatable even with Polybian units, as the following experiment will show. 40.000 Mnai was the price. I was left with 3.000 and the AI, 300, and they had a 19-stack. 3200 Macedonians vs. 3000 Romans, roughly. Hard difficulty.
And the successor army was shamefully slaughtered. But hey, I think it was you Dayve who was quoted as saying "You're fighting the AI, how could you NOT win?"

Spoiler Alert, click show to read: 


I didn't even need the Accensi, bloody useless. It was the Triarii that won the battle.

My first battle with the Romani, by the way... only noticed this after it was over.