In short, Brando was good in some movies and in the most talented hands of most capable directors such as Kazan and Coppola especially Kazan who directed him in Streetcar and was a seminal part of the Actor's Studio, the drama school that Brando came out of.
But to go overboard on Brando as a "genius" based on a body of work that is very uneven betrays the fatal attraction that Hooywood types have for self destructive anti social and and so called anti establishment types.
I had the TV on while Penn was on Rose, but in the interest of good mental health (my own), the volume was off. I noticed the self-conscious suffering on his face, though, and the bad boy cigarette between his fingers. He's a tiresome bore. The whole anti-hero thing that Brando (and Dean) ushered in, while it may have once had its uses, has gone stale. And Penn is the proof.