None of the ones I had were hard keepers, sometimes they have ulcers if they've been in racing but once treated and they get a settled routine in a normal environment they seem to be OK.
A mare we bought that had raced at Goodwood (UK) only days before had about the worst worm burden I've ever seen.
They don't always do as well as hardier breeds wintering out without a blanket/rug in colder climates unless you feed them 'both ends' but seem to cope better if you stable them in bad weather if you don't want to blanket.
This is one of the last OTTB's I had and he pretty much lived on his daily turnout on not great grazing, no more hay than the cobs and a small feed of beet pulp, chaff and grass nuts. If he was competing he got some micronized mixed flakes which we get in the UK - steam cooked oats, barley, peas, beans, wheat & soy - but not a lot, just for some extra energy. His biggest fault was like a lot of TB's - he had awful flat feet - not great feet in general and could never work without shoes but one my husband had came with bad feet but they improved so much he could ride on roads barefoot.
I don't know much about pintos & quarter horses - other than my pinto that has no history is probably a Paint so is likely a mix of QH, TB and whatever else goes into them. Over a short distance she is full of life and go - she's so light on her feet - but on a longer ride our cobby types are still going at the same speed while she's struggling a bit so I have to work harder at keeping her fit. My TB X welsh cob who's now retired pretty much would still be going like the same nutcase at the end as she started out as - I could never wear her out.