well the Fms are awesome, and unlike mounted non-nomad FMs you can have a large amout of them in one stack without the army getting silly and ineffective. th great disadvantage of the KH(in terms of FMs) however is that they don't have any lancers until you either hire some Illyrians or upgrade Athens*' MIC. Most other factions get Lancers early on due to their Bodyguard being a lancer. Exceptions here are sweboz not sure about saba and Lusotani, aka how lancy their cavalry is.
And Lancers are of premium importance when dealing with superior Infantry formations. With some good slinger use it's not that big of an issue but It does throw soem people off. also Having a foot FM means you won'T be able to kill most of the routers. :(
The heavy cavalry FM of other factions can be a winning force in battles as well with some charge and withdraw micro, but imo are less useful in a less developed army.
you're right there, If you don't have anything to hold the enemy in place it's not so easy to strike at them. However apart from the nomads you usually have a unit or two of phalangitai or other heavy infantry in your army to pin down them buggers.

PS: ehm, what was the topic anyway?^^

*or a more nothern city when you blitz a lot