This is arguably the weakest cavalry bonus of The Last Khan’s civs. Compared to +25% attack rate? +1-4 damage with relics?
Meh.
Cumans get a good early game, yes; but even with a slightly buffed Kipchak (I’m still in favor of +1 to all Cuman CA in Imperial Age) they still have lackluster siege, no defenses, no navy, no bracer.