It could also be possible that it has happened before though...
They did mention that they had previous summoners from other worlds too..
And do you really think NONE of them thought of beating up their summons and doing so?
Many will most likely take advantage of the fact that summons can't harm the summoner and that they must ALWAYS protect them no matter what.
Then again, they could also still make up an excuse (the summons) that they're only beating the summoner up so they could "protect" them by helping to stop them from acting abusive since it could one day backfire against them(the summoner)..

I wonder just how much emotional damage it would do to a summon of their summoner beat the shit out of them? Or even just decked them for pissing him off… I don’t know if we’ll ever see that, but I am curious.