He can hit pretty hard, but he's slow. I'd recommend at least the rank 2. He actually carried in the mutant quest of this months TB EQ for me more than Kitty Pride and AA. He has a pretty decent heal on each special, hits insanely hard with the sp2 with his sp3 fury, and he ramps much faster against non-robot bleed immune champs.
Even unduped, Namor is a very solid damage dealer. Not any utility, though. So, if you're looking for a Mutant damage dealer and you have an undeveloped roster, he might actually be very useful to you, even unduped.
Comments
TLDR: I wouldn't rank him.
Namor's awesomeness is largely based on a very high signature against specific types of matchup.