I do think they should be nerfed just a little bit. The advantage of heavy foot heavy with the +1 to cohesion that aid them in holding out better over the long term typically can't, in competitive multiplayer, compete with the medium foot advantages of being cheaper, more numerous, more maneuverable, and not being disordered by rough terrain. Especially in Classical Antiquity where there are a lot of decent medium foot armies. It seems like the current balance is geared more toward singelplayer campaigns where the AI and more novice players don't use the maneuverability and greater numbers of medium foot to maximum advantage, but in multiplayer I think they are OP.
If you look at the army statistics page, there is a win percentage table for I think seasons 1-4 or 1-5, and the top armies tend to be medium foot armies, ranging from having a very large number of medium foot (like Carthaginians or Romano-British), to being outright medium foot spam lists like Bretons, Jewish, Samnite, Spanish, Scots-Irish and Picts. Massed Archer armies are also up there but have since been nerfed (I can't comment on the Chinese lists because I don't know them well). Lebo44's statistics support the same conlusion:
viewtopic.php?f=501&t=98309
It should also be noted that armies which feature large number of cheap low quality undrilled heavy foot like Egyptians, Kingdom of Soissons, and Arab City 300 also do quite well, and I suspect it is to do with the general strategy of cheap infantry spam being a bit op. It's just that most infantry spam armies are with medium foot and not undrilled heavy foot.
A few Hellenistic armies also do pretty well (they're not in the top ten but they still do ok), but that could be because one or two of them are heavily favored by some of the best players, or because pike lists have very few pikes and supplement with pretty large amounts of medium infantry as well.
I don't think a big change would be in order, but perhaps something small like an extra -1 to ct for mediums against non light cav in the open, or an extra poa to cav in the same scenario, or a very slight (2-4 points perhaps) increase in cost to medium foot units might be appropriate. I would be willing to mod and test whatever in that regard.