Is jumping over crossrails harmful to a horses joints?

I have a rescued paint that LOVES to jump, but isnt conformationally built for it. My trainer keeps saying that if I jump him it will break down his joints extremley quickly and leave him lame. So my question is will jumping him over cross rails to maybe 2 ft tops once or twice a week be harmful to his joints? I would ask my trainer but I don't want her to think I am contradicting her.

He will be fine. I have seen horses much worse off comformationally jumping 1m+ courses thier whole lives with only the usual wear and tear expected.

Just make sure he is fit and healthy and enjoys doing it! Goodluck :)