The bones or lack thereof are complete fucking irrelevant. I care about the fact that;

A very strong and skilled swordsman, younger and presumably stronger than Bard, two-handing a greatsword;
makes a damn near perfect swing from a stable position;
and Bard, who is not superhuman by any stated measure, just one-arm blocks it at near the strongest point of the swing like he's blocking a kid's punch.

Even if it didn't break through the armor, the sheer force should have ragdolled Bard out of his saddle onto the ground.