Because Zoro cant deal with a sword, as swordsman, is pretty much his own fault, not the one of a sword. If he is to weak to weild a sword, dont blame the sword.
Zoro duels with Sanji all time.
But also, i dont know why "trained by wss" has to include shanks in any way. Shanks is clearly above Mihawk, like Rayleigh is, like Admirals are, like Luffy already is, like Roger was etc. pp.. Just look at what Mihawk delivered in Marineford. Oh yes, nothing.
Whole one piece is the plot.
You poor little boy are mad because Oda doesnt write the edgy story you need to?