No, not at all. His skill is practically above Yonji's (clearly seen when Yonji's face was fixed by a doctor since it took a lot of damage) Not quite sure about his level vs his older brothers and sisters. He's one of the strongest in Germa 66 not only as part of the infamous family but as an individual.

Sanji would have beaten Judge if he wasn't caught off guard by the human shields. He was holding his own until that point.

For me Sanji isn't really that strong , compared to Luffy and Zoro. He needs a power boost badly in general. But that's just my opinion...

In my opinion he's super strong but not quite. Because i know after this arc sanji will reveal his true potential. I'm sure he can beat niji and yonji but not reiji and ichiji and honestly speaking. Ichiji looks super strong bruhh