Regardless of whether it would make Old Ben overpowered or not, how in the Galaxy did they fail to give him taunt?
He's the only character in the movies that specifically invites attack in order to prevent attention/attacks directed at other people.* That's taunt. An Old Ben without taunt, when lots of other characters have taunt, is just ridiculous.
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*others engage in reckless attacks, of course, but a frontal assault isn't a taunt, per se. Old Ben clearly invited Vader's attack and thereby focussed attention on himself. His glance at Luke shows that he meant this to happen, that he meant attention to be diverted from Luke and the others. That's very different than Han Solo valiantly but stupidly charging some Stormtroopers.