You want him changed so that he doesn't slow matches to a crawl. That is his character. He's got tons of health so that he can take big risks to get in. You're not doing a lot of damage to gief, typically, because you're not landing a lot of combos on him. That is the archetype. There is nothing like that in SF5 right now. I don't know how you'd retool him, but we already have a fast, mobile grappler in Mika. Making him play similarly to her would be redundant, it would take away the type of grappler that Gief is supposed to be, that was created with him.
Like I said, he slows matches to a crawl because you have to be patient fighting him. He can kill you in a few grabs. In SF5, that'll be exacerbated, I'd guess.
And I would also argue that Rufus doesn't bring anything particularly unique to the table. He's a different kind of offensive because of his divekicks, but he's still another really offensive character in a long line of them so far. So while he brings diversity in his playstyle, he doesn't diversify the cast in any unique way the way Gief would.
