Spear throw really is just an enabler for extra XP, the damage is trivial. That's why they're bonkers in Shaka's hands, because of his reduced thresholds for leveling. Without that... it's a nice perk but nothing too strong.
Honestly what has me more concerned is the rather high retreat chance. Knights can be incredibly tanky for their era as is, I'm really not going to appreciate half my attacks just not doing anything (or worse, helping them retreat out of range of my other units). Combined with something like the new overrun, Knights seem like they can just blast right up in the enemy's face, do a ton of splash damage, and probably get out alive. Certainly breaks stalls, but it seems too much.
Poor University of Sankore is going to need a buff too now that it's brothers are must-builds.
Impi spear throw is basically double damage, it's an extra attack before melee, same here with cav.
If you play on very high difficulty you will maybe not notice it as much but I've even seen diety play where Impi really shone despite them being a backward tech unit.