Dude, I literally agreed with you that the Sanji & Luffy vs Kizaru setup only to get Sanji run next chapter was a low blow from Oda, I was really looking forward to that.
But I kinda get it. I joined the forum at the peak of Yamato vs Carrot nakama wars, and I was really disappointed with how Sanji was treated, and whined so much in the threads that I got accused to be someone's alt and a fake Sanji fan.
So I've been there, where you are now, with Sanji being humiliated by Black Maria, shut on in his own arc, being called a dog.... At some point I just realized 1) I'm expecting all the wrong things from Oda and 2) it's been always Luffy piece, it's just that the awesome fights like Luffy vs Lucci are a thing of the past and we're stuck with looney tunes now.
Now, I STILL like Sanji's character. He is my favorite SH.
I like that he's more complex than others. He still has some development even after 900+ chapters, character-wise (I'm referring to him asking Robin to help - yes, it was humiliating to see him helpless, but it was legit character growth compared to WCI "I'm going to sacrifice myself because I'm anyways pathetic" to "actually, screw that, I've got friends who need me and who I can rely on, I can ask for help"). Him choosing his humanity over Germa power? Peak. I am interested in his story more than in Luffy's. And even though I hated how Sanji got robbed his Kizaru fight on Egghead, he still had a lot of cool moments anyways.
So I get your frustrations very well, I also had them, and actually I still have them, because I want Sanji to shine, to deliver another Mr.Prince moment, to fight Kizaru and win, to unlock CoC. It's just that I understand that Oda will never deliver, so I am more chill, and don't expect much.
TL; DR don't expect much Oda, save your nerves. I''ve been where you are, and letting go of hype was the best thing I did.