Actually, I think the portrayal of the KH is brilliant. Problems with hoplilte dominant armies vs sarissa-phalanx armies? Check. Crap cavalry? Check. Disastrous foreign policy as a result of impractical ideals of Greek freedom? Check. A poor heartland unless you can actually make yourself the center of sea trade? Check. Rhodos being the economic engine to the mainland's source of troops? Pretty good. (I have no idea what you mean about them being a drain on the economy. In my campaign they gave the most tax revenue and the most trade revenue - and that only improved when you get to trade with Halicarnassus.)

The Antigonid dynasty never held all of mainland Greece, and Pyrrhus did march into Macedonia proper and make a play for the crown... so... well what's the problem? Lol.

The only big ahistorical problem with the KH is that it doesn't fracture and disappear if the player achieves real military success. The KH was economically and militarily crippled in history, so that's good. Rhodos was really the only player among the KH homelands in our time-frame. And that was just in terms of trade, some naval power, and maintaining independence for awhile. If you conquered Hellas all the way up to Pella, you're already beyond any historical segment of the campaign - now its just a question of how far you want to take the independent Greek city-state alliance fantasy world.

You should take it as a role-playing miracle that the gates of Pella were opened. The local Makedonian notables probably would have been happy to do so to get rid of the effeminate southerners in favor of a dynasty that would respect their traditional privileges.