Horse archers can be quite annoying for most civilizations because they are very mobile, but HRE isn't as threatened by them thanks to the additional movement speed on their infantry.

Against HRE with Regnitz Cathedral, as Rus you cannot afford to let them get even a single relic - you need to contest all relics aggressively, otherwise it becomes extremely difficult.

Rus is stronger in the late game due to better composition and passive income, but if HRE secures three or more relics, that advantage can flip completely.

HRE can put relics into towers to generate gold and provide defense, making their base nearly impenetrable to horse archer raids.

Rus horse archers do significantly less damage to HRE knights thanks to the additional +2 armor from Meinwerk.