Schwarzer Reiters have been weird classes to build for due to their main weapon, the Pistol. Pistols do not work with a large majority of Archer tree skills, meaning you would have to rely on weapon swapping.
Another disadvantage on top of this was the fact that all Schwarzer Reiter skills are mount-exclusive, which also makes it hard for some classes to synergise with Schwarzer Reiters.
However, with the recent 20th of Oct patch to kCBT3, Pistols are now counted as Subweapons. This means they can be equipped alongside a Crossbow, which opens up a large majority of skills for them to use without the need to weapon swap!
Please refer to here for skills which can’t be used whilst mounted.
Almost every skill which can be used with a 2H Bow can be used with Schwarzer Reiter now, thanks to the addition of Crossbow usage! (e.g. Multishot, High Anchoring, Barrage, etc.) All Fletcher skills require a 2H Bow to use, so you will have to weapon swap to use their skills still, and take note of the skills which can’t be used whilst mounted.
Nothing stops you from weapon swapping or dismounting, but for people who want to play Schwarzer Reiter with fluid synergy, now is the time to do so. This should open up the possibilities for more fluid Schwarzer Reiter builds!