That clash was pretty even. Sanji tagged him, but he also messed his leg up, while neither went all out. Sanji didn't use Hell memories and Vergo didn't use Haki and bamboo
Man I see this argument hundreds of times, kind of tiring to see it repeated.
I just came from the sauna about an hour ago where I do shin training, beating my shin with a meditation bowl stick I bought Yeah I know, I do that kind of stuff...(it gets boring in the sauna)
What I noticed is how my shin is much stronger the higher up I go, because my leg gets thicker and muscles thicker there. My ankle is extremely weak when I beat it and it hurts a lot because it has weak bones and muscles. It is a very weak part of the leg.
Now Look at how Vergo and Sanji clashes
Oda is literally having Sanji put up the best defence and Vergo put up the weakest kind of attack where he should be the one breaking here, not Sanji!
If Vergo broke Sanji with that clash, it must by necessity mean the other clashes we see Vergo do where he has legit poses, stances and kicks WERE NOT SERIOUS because those have more breaking power because of added hardness and power. This stance is very bad (and omg do I have to repeat the shit about the right leg, you know what look that shit up yourself: Vergo kicked with his right ankle, not the left).