Sanji was treated much better pre-timeskip, but I'd say since Wano things have been much better, as far as fights go, for Sanji than most periods post-timeskip. Sanji had the S-Shark clash where he looked good though unfortunately the conclusion or lack of one was off-panel, not to mention he's gotten a few feats against top-tiers before getting overwhelmed. Sanji's not a top-tier yet, it's understandable that he'd struggle.
I think his performances could be better, but he's not exactly flopping this arc. He succeeded in saving Bonney by dispersing that light-beam and kicking V. Nusjuro, he just isn't strong enough to maintain a 1v1 confrontation against either right now, so he got overwhelmed. The only iffy part I feel is Vegapunk dying, but honestly Sanji was also with Luffy, and it didn't help that the guy had been stabbed prior so they had to hesitate considering he himself was telling them not to run with him initially. It's definitely a failure, but it's kinda an L that Luffy and Sanji share.
My only real gripe is that the S-Shark fight was off-panelled, Sanji went from just getting stare-diffed to leaving Kizaru shocked and roasting Nusjuro, losing against top-tiers ain't the biggest disappointment. He'll continue to progress from here, and we'll probably get more on the eyebrow flip and the power of love in future conflicts.