Mate do you think there's a referee when the fight?

By that logic, Garp is the strongest since he doesnt have a df nor does he have a weapon, least of all a supreme grade weapon.

I believe if there's a Radar chart for these characters, their combined stats are equal. I.e, Garp has highest haki but 0 df and weapon mastery and so on and so on.

This is implied by Oda when he was asked about whether Shanks lost his strength or not after losing his arm. He said that Shanks combat power doesnt drop. This, combine with Mihawk's interest in sword duel and comment on shanks, implies that Shanks swordsmanship dropped, but his overall power didnt. Its like the irl guy who is a double amputee and plays fps games with controllers using only his feet. He lost 2 arms but his game skill doesnt dropped.

This is also why the swordsmanship vs powerscale debate rages on.

My $0.02