Try to remember back in Brawl, down throw had more horizontal launch than in this game. What I'm trying to say is that if diddy's grabs were nerfed to the point in brawl. Fairs would be your only follow up option and thus completely removing the Hoo Hah!
There's nothing wrong with Hoo Hah...
It's the fact that Diddy has it IN ADDITION to his infinite amount of tools, mobility, sheer power, spacing game, pressure, the speed of his combo and kill moves, banana guaranteed setups, autocanceling aerials, popgun reverse canceling, onstage game, offstage game, mixups, safe landings, the uses of the banana, kill throws, punishing, etc.
He's a REALLY good character, but people can only think of Hoo Hah. If Hoo Hah is OP, then we should ban Ness for having a killing back throw and comboing down throw, or ban Luigi for his D-throw -> anything he wants combos. Hoo Hah is not the problem.