D3's high tier matchups are like perfectly even. He beats Lucario with an advantage, Even for ditto (LOL), loses to zero suit with an disadvantage, even with game and watch, and even with toon link.
I would agree with TC, D3 will probably be able to gain life again. He does well against Snake and Marth and can compete well against them (Pretty better than others can). Also the Wario matchup D3 does good and imo is Wario's worst matchup.
The only downfalls (Which is pretty much just balance and weaknesses like the others have) is going to be ICs, Falco, Olimar, and Zero Suit Samus.