I don't know if ineffectiveness is a form of abuse .... but nope I can't say that I can think of anything that is worse than abusive training technique. I think that most of the people out there are not deliberately abusing but where I live there is quite a lot of ignorance when it comes to teaching horses. So I just thought I would put it out there and see what people came up with.
I know someone who is good on the ground but not very good in the saddle. She's too strong on the ground and too weak in the saddle. She causes problems because the horse will lose confidence and also gain some dominance.
But then I know of someone else who starts horses here and he is quite abusive and actually "drags" them through the trails with chains around their noses while riding another horse with a roping saddle.
So in this case I would say that starting a horse out with chains and dragging is something they may never get over but having someone get on and cause a few problems is not a big deal.