I learned, at least for myself, that sparring with people better than you gets you to learn and adapt faster. You also learn from them while fighting, and pick up stuff that they are using and also adapt to a better opponent and become better yourself.
Thats why I always liked sparring instructors - yes it is more unpleasant, and you are getting ht more, but you are learning more and faster while doing it - you can really notice the difference if you go back to sparring with your peers afterwards, how much easier it seems.
Trainers also have to have sense how hard they want to push someone new - if you feel your ribbs the next day, or/and have a couple of bruises for the next couple of days, just eat it up, it is part of the training, and it is making you tougher, I don't however advocate wrecking the crap out of the new guys so that they can't walk for a week afterwards, because injuring them is putting them off training, and also discouraging them before they have the chance to adapt.
