So, a dark type T-Rex with 100/134/119/95/100/61 stats, the ability to produce one of the best weathers in the game, an extremely wide movepool and a consistent ranking in the top 5 of the standard metagame tier is not a good Pokemon? I mean sure, he has lots of weaknesses and dies to Fighting priority, but he also wrecks stuff, can serve as a Pursuit trapper, revenge killer, set up sweeper or banded sweeper, can get a hefty Sp. Def boost just by coming out of its Pokeball and provides permanent sandstorm. If you don't like him, that's fine, but he's not mediocre, he's an excellent Pokemon.
What about Hydreigon?