I don't he know about the legality part, but Justice KBJ is clearly not as smart as the other justices.
I think liberal justice Elana Kagen is actually very smart/brilliant, even if I disagree with her on many issues. Her opinions seem reasoned and articulate.
Justice Sotomayor, to my mind, seems to be a Mrs Potatohead compared to the other justices on the court.
But then there is Ketanji Brown-Jackson, and she seems to be a box of rocks compared to the Sotomayor, which you would think would be hard to do. KBJ seems to excel at being the clear and overwhelming winner in the competition to have the least reasoned opinions of 9 justices and simultaneously also having the least articulate questions, but simultaneously she has the highest frequency of (inane) questions..