Ok, I think I managed it. In my HRE I sent princesses, spies, and emissaries over to Spain to see how things went.

In 1118 Spain conçuered Cordoba, but this was not because of overwhelming numbers of Spanish Jinetes, but rather, an extended royal family. The number of Jinetes was 6, two of which were in Portugal as garrison. Their combat army was composed of 4 jinetes, 4 royal knights, one unit of archers, and several Urban Militia (since in the Pocket Mod there are no peasants). I think the the almohads retreated, as their Khalifah was there, but afterwards they made several attempts to recover Cordoba, which failed, but dealt heavy damage to the garrison Spanish army. It wasn´t until 1150 when they finally managed to get hold of Granada. AFAIK Morocco still holds, so the Almohads might yet resurge, if being kicked out of Spain doesn´t trigger a civil war.

So: the nerf was increasing the production cost to 300, and the support-per-unit to 90. Apparently it worked, as the limited number of Jinetes in the Spanish assaulting armies seems to point out that they were not the main factor.