The main problem is not Sanji's portrayal in post-timskip per–say, but the raid suit. If Sanji defeated Queen whiteout raid suit or with a normal power up then all of post-timskip would pay off, pay off quite nicely to be honest. But raid suit has completely killed Sanji, raid suit is the worst thing an author can do to a character, it's absolutely disgraceful and disgusting. 🤢🤮😡
First of all, it completely changes Sanji's fighting style, 800+ chapters were thrown away, it's the same thing as deciding to rewrite a character when the story is 80% complete. Sanji's fighting style right now is the "hide and hit" when Sanji turns invisible and kicks his opponent from the blind spot or back, it is absolutely disgusting to watch, it's not even funny.
Raid suit is too OP, it's so powerful that if that thing had brains it would be able to defeat Queen just by himself, it doesn't even need Sanji; raid suit is tough enough to withstand an attack that would otherwise just kill Sanji plus it has barrier ability just like Bartolomeo; raid suit makes Sanji invisible like Shiryu, it also increases Sanji's speed; raid suit allows Sanji to fly which makes sky walk (the only thing he learned during time-skip) completely useless. Is there anything that raid suit can't do?
And finally, raid suit is the ultimate proof that Sanji is indeed a failure, Judge was right all along. The moment Sanji accepts raid suit as his permanent power up is the moment when he will accept himself as a failure and become Judge version 2. Either Oda is stupid enough that he doesn't understand it or he does it intentionally to humiliate Sanji, and I don't think that Oda is stupid.