Regarding peanut rollers: I bought a halter-bred APHA weanling for almost nothing (QH on both sides) because she only had a belly spot (she’s 24 on January 3). Both parents were tall so I assumed she would be at least 15.2hh for the hunters or eventing. Unfortunately she’s 14.3hh .
I backed her and did all her training myself from day one. She naturally had a normal English-horse headset and big gaits with good over track. So QHs can easily compete in non-Western sports—although those starting as a blank slate are probably easier to work with.