I'm trying to ensure I train horses specifically in the discipline they excel in (eg. my PEP geldings train XC specifically etc), but I'm finding I'm having to hire a lot of riders to cover all my disciplines and levels to have riders training in the same discipline as my horses. Is there any massive benefit to this, or should my riders be all-rounders with horses training individually? Or even have my horses all train in all disciplines?

If you don´t want to micromanage your riders and use only "all discipline" riders on your horses, you can safe a lot of money and the show results or training efferts will not change or only very slightly.

I use all discipline trained riders for over 9 real life years now and my horses always placed well in shows and earned tons of ebs ;)