Senatorial gravitas?

I hear Senate incumbent Raphael Warnock (D, GA) says challenger Herschel Walker (R, GA) will not be able to cope with the cognitive demands of being a Senator.

What is Warnock’s opinion of John Fetterman’s Senatorial capability? Was he ever asked?

Should Mehmet Oz have used this tactic against Fetterman in PA?

If not, why not?