Yes, there should indeed be counters to fast units. Yet I think that many, if not most, of these counters already exist.
Also, everything counters itself.
I think the main focus here is to have, say, an all archer army not always beat an all melee army.
but A) I just don't see bows being strong enough to do this, no matter how useful kiting is
and B ) An all archer army should always devastate all melee ... until the melee catch up with em
I think the concept of not being able to Kite a very slow unit would be bad ... unless the unit doing the kiting is just stupidly OP.
I do not want archers to be either too weak or too strong, but I don't mind a hero-archer kiting a big scary monster as long as it does not happen under normal Warfare-with-Faction conditions.