I have done both. My old account I had probably 800 showing horses that were a mix from all my different breeding programs. I just restarted so I'm going to play around with SD while I build back up
I don't really want to cull all my geldings as I think I will lose a lot, but maybe I need try SD. I have noticed training seems frequently skewed with my AD horses.
I haven't used that method before but my guess would be as the horse goes up levels it gets less accurate. When a horse is level 1 or 2 and weak in movement for example it's probably only down 1 or 2 bars comparatively and will still do well. But when they get to level 7 they could be down in mvt by 3+ bars and it gets skewed