All this talk about who stronger than whom; is all relative.
It's about the different match ups that one faces.
Enel, can be considered one of the strongest logia users; especially down below Sky Island because his use of electricity (water is conductive). However, Luffy was his natural enemy. IF Enel defeated WB hypothetically; it does not mean Luffy can defeat WB just because he defeated Enel. Those two circumstances are independent of one another.
The same can be said about recent events, does not demean the status that Mihawk is the strongest swordsman but just illustrates the fact that he might be meeting his rock against one of the WB captains.
On a side note, where did Garp go? Wasn't he next to the old Marine women?