I think men are saying this stuff because they've gotten so weak over the past couple of generations that it sounds plausible.
Grip strength is seen as an objective indicator of morbidity and disability. However, empirical knowledge about trends in grip strength remains incomplete. As trends can occur due to effects of aging, time periods and birth cohorts, we used hierarchical ...
www.ncbi.nlm.nih.gov
Still, when you compare elite women's spike speeds to NCAA men, men spike about 10-20 mph faster. For the same mass of volleyball, this is a kinetic energy difference of 6-25% against a 10-20% smaller womens' size and lower net height. Also, men are used to hitting a ball with a larger circumference, so the kinetic energy difference of a man hitting a woman's ball would be even greater due to less wind resistance.
If he's too weak to play against other men his age, too bad. That doesn't mean he should be playing against women nor should you be defending this (repent).