If Rogi had developed his 2 hander I think he would have amassed well over 20 slams.
His form and technique is solid.
He definitely would have been able to defend much better against Rafa's big forehands on clay. He could still hit piercing one handed slices and droppers as well. Dual weaponry.
25 slams, GOAT status secured. Well above Connors/Borg/Lendl/Delpo.