Hm in my Dom2 TienChi games pikemen worked well against heavy cav. Though i see them more as chaff with increased effectiveness against cav, than as real cav killers. They're worth the extra cost overstandard militia imo, though of course i'd prefer gladiators for the task.
They don't perform so well vs. artillery, but that's what the footmen with towershields are good for.
But i agree that Dom3 could use some real anti-cav units. Maybe instead of improving the pikemen, add another better (consequently more expensive) pikeman to the nations that have them, with enough stats to actuall get that repel working reliably. (say, 30-40% of the time against heavy cav, less against knights obviously)
I see a possible balancing problem, since they'd also be quite effective at repelling other infantry, which shouldn't be the case with pikes, but then, without shields they'd be quite weak against artillery, and high morale can at least make the attacks connect.
Hmm, maybe (for TienChi) something comparable to the heavy glaive troops, 14 protection, 7 defense, but 13 attack and 15 or 16 gold costs (and 18 ressources). And a pike obviously.

Or as an alternate route, maybe change the pike's stats from 1 att -1 def to +4/-4. Will not exactly increase the pikemen's survivability, but make them chaff that actually hurts heavy cav while taking away their charge bonus. Heck that's even more realistic. While pikemen could skewer charing cavalry, those 1000kg of horse, rider and armor didn't stop dead just because there were a few pieces of wood stuck in them. And a horse rolling over you hurts.