I know I won't be able to get a solid answer and I could always just change this detail depending on the setting etc., but in a realistic scenario, I have no idea if they'd be significantly stronger than typical humans.
For a normal human, I could do a lot of guesswork since someone's legs are supposed to be 2-3 times stronger than their arms so you could get an estimate of a bench press from how much someone can squat. Problem is that we can't put a barbell on a horse and make it squat. Not to mention the rear legs are supposed to be much stronger than the front.
So I think the next logical step is to consider proportional strength but I don't even know how I'd be able to do that.
So is there some way to get a good idea based on a horse's power?