Sanji has never actually had a fair fight since post-TS, whereas Zoro has been facing opponents much weaker than Sanji has. Pica isn't stronger than Vergo either.
Not to start another endless Sanji-Zoro debate, but i disagree here. Hyouzou > Wadatsumi. Fujitora > Doflamingo and against Wadatsumi, Sanji had Jimbe's
help and against Doflamingo he had to be saved when Zoro handled things on his own. It's the rating between Pica and Vergo that i'm unsure yet, but eventhen.
Vergo got the upperhand in a shortskirmich against Sanji using his own leg-fighting style, without using his bamboo staff and haki when Zoro fought Pica much longer without receiving a scratch and is shown to be on another level despite actually not going all out(well at least until yet), so regardless who is stronger between Pica and Vergo, Zoro is clearly shown in better light and same concerning other fights since the timeskip started. The truth is Sanji didn't really have a 1 on 1 fight since enies lobby. He was either in group or duo, or getting small skirmiches that didn't always end up well. Not to mention that in terms of stats that we know so far, we have
Fire Power
Zoro > Sanji(1080 Pound Phoenix, Crossing of the six paths or Shishishisonson is stronger than Sanji's greatest move(Hell Memory) and we've yet to see post-skip Asura)
Stamina
Zoro > Sanji(Considering he had better stamina preskip, it should be the same)
Durability
Zoro > Sanji(like above)
Top Speed
Sanji > Zoro(sky/blue walk gives Sanji the edge)
Reaction-speed
They are equals give or take
Close quarter
Zoro > Sanji(mainly due to the range of the swords)
Range
Zoro > Sanji(Sanji having no range attacks)
So Zoro beats Sanji in practically all categories