Actually, thanks to Lucy, we have a filmed record of the levitation magic act Welles was doing in Las Vegas, and as we all know, Welles liked doing magic tricks. He even did his very own TV show (THE MAGIC SHOW), plus he liked Lucy personally, so why shouldn't he do a guess spot on her TV program? Just because it's not Shakespeare?
By that same logic, Welles shouldn't have wasted his talents on making thrillers like TOUCH OF EVIL or THE LADY FROM SHANGHAI, either.
Of course, the comparison with Robert Wise has some validity, since in the sixties Welles was directing crappy films like THE TRIAL and FALSTAFF, and Robert Wise was making such musical masterpieces as STAR and THE SOUND OF MUSIC.