You didn't prove shit with those panels bud.
Oda didn't establish any of that shit. Only in your head has the establishment been made that not leaving cuts somehow correlates to swordsmanship. What he has established is:
Just be cause you use a sword, doesn't mean you're a swordsman. You can use swords and not be a swordsman:
He has established that Roger was not a swordsman but a haki master:
Shanks and Roger are not swordsmen in any sense. They're hakimen.
Shanks title is literally hakiman if we go by the "killer of observation haki".