People keep saying he's the new Usopp or that Usopp will surpass him without explaining how Usopp has improved post-timeskip. No point in comparing if you're just gonna list what's bad about one of the guys. I'm not against Usopp becoming stronger than Sanji (well, I am but it's not impossible) but it seems strange how no one's explaining how Usopp has fared better than Sanji, after the timeskip. Sanji's warm-up fight ended up being the guy Usopp's been focused on in Onigashima so how exactly does it look like Usopp will surpass Sanji? I want the best for both of them but if we're comparing then that's what should be done. If we're saying Oda doesn't like Sanji by comparing him to Usopp then I disagree, Oda likes both, it's simply expecting the wrong thing from the characters.
There's no point in just listing Sanji's failures and saying that proves Oda is purposely humiliating Sanji. I feel like this is just expecting other things from Sanji that just isn't him. Of course he'll look bad against Viola (who he ended up making switch sides and helping the Straw Hats) and Black Maria (which was meant to showcase Sanji trusting his crew and to give Robin a moment). It's not Oda purposely humiliating Sanji because the guy is versatile, there's a lot Oda can do with him.
Obviously he gets the short end of the stick at times like when he was used to hype up Vergo and Doffy but the only reason he was used is because he's strong. No point in Doffy beating anyone aside from the top 3, the story gains nothing from that (it wouldn't hype up the villain) so Sanji's used. Oda tries to make up for it with brief clashes like Sanji kicking Oven into a building, Sanji blocking Daifuku's giant genie, Sanji, with help from Luffy, blocking Big Mom and Sanji kicking Page One around. We all have our own interpretations of these events of course so it's possible these are all bad performances to you and that's fine.
In regards to everyone seeing Sanji as Germa, that's the point. That Sanji isn't finished with them even if he wants to be. He's meant to continue running into people that see him for his family because the plotline isn't over. He's meant to put on the suit despite the fact he hates Germa because he'll be tied to them until this plotline is completely resolved and it's meant to be him putting his pride aside to help however he can (helping the town's people from the guy hunting Sanji despite no one else in the alliance wanting Sanji to or him saving Momonosuke from King and Queen after Shinobu failed and no one else was in a position to even try).
Overall, I can't blame you for clowning Sanji. It's understandable. He has a lot of shortcomings but saying the author is purposely humiliating the guy seems like an exaggeration but it's your interpretation of course. Sanji still clashes with strong opponents and if he beats a strong opponent this arc, I don't see the problem. Of course, only time will tell if Sanji does.