What he fails to understand is that if you are holding hard there, it means that you are open somewhere else. that "anchor" is his failure point. He believes that by applying as much force as he can there he is controlling you, more force, more control. However, it is not correct and he has an weakspot somewhere else.
Tell him to losen up if it hurts, first of all.
Secondly, realize that you are not a failure by having him do this. See if you can find the weakspot.
I've been doing this long enough now that I can find it pretty quickly...also, I never grab to hard like this as I know that if the other person is good, I just comitted a tactical error!
When someone grabs like that, it usually is telling about there level of experience and skill. so keep that in mind when looking for your own validation of training!
What he said. People who are trying to control you by using a lot of force on one place, focus on that one spot and often forget that they are wide open for jabs, kicks, punches,... A quick atemi might startle him and cause loosen him to loosen the grip a bit.
Oh and your ego is not worth bent or broken bones. Just tell him if he's squeezing to hard.