Are there any other showings of him doing anything remotely the same to another character? Namor went toe to toe with Sentry. Even though he was being pushed back he was still holding his own. He also fought Blue Marvel, and was doing well.
Someone had to pick apart that scan, because Diana wasn't ready for the fight. It began in Bizzaro's favor (sneak attack anyone?). Bizarro has been defeated by less than Diana before. We can go by full capacity in terms of abilities, but combat averages have to be taken into consideration as well. Namor's superior fighting skill, and power to deliver crippling strikes to weak spots is something else that shouldn't be overlooked, That scan is misleading.