Even Pre-TS, Sanji didn't have fights like you imagine, seriously
In His Introduction Arc, he didn't defeat anyone, his Arc was mostly again about his Kindness & learning from Zeff/Luffy/Zoro
In Arlong Park Arc, all Straw Hats fought including Usopp (Nami doesn't count here)
In Little Garden or Whiskey Peak, Sanji was again without Fights
In Alabasta Arc, he fought just like all Straw Hats
In Sky Island, Sanji only finished Satori with help of Luffy & Usopp & after that he didn't have any fight, he actually got off-paneled by Enel very early & wasn't among the last ones standing (This Arc clearly showed difference between Zoro's Role as Main Fighter & Sanji's Role as Hero)
Ennies Lobby Arc, he fought Jabra just like every Straw Hat had a fight
And in Thriller Bark, he fought against Absalom but he was Weak & Nami was the one who finished him
And then he fought against Oars with everyone else
Finally, he fought against Pacifista with all Straw Hats
Conclusion:
Sanji's Only Major Fights were against Kuroobi, Mr. 2, Jabra, Oars & Pacifista & all these fights happened at times when All SHs fought.
In other words, Sanji is no different than rest of Straw Hats when it comes to Major Fights, the only difference is that he saves them more from Fodders & always act as Hero doing very important Tasks (Ennies Lobby Door, Mr Prince, Enel's Ship, Wedding Cake ... etc)
And the same thing applies in Post-TS, Sanji is a Hero who saves his Crew, his Family multiple times ... etc Oda doesn't need to give him Major Fights when other Straw Hats don't have any because the Fighters who can't do anything but fight are Luffy & Zoro (Outside fighting, they are useless) but when all Straw Hats fight, then Sanji will be given a good fight & better opponent than rest of Crew aside from Luffy & Zoro