Trust me, Dolphure isn't overpowered. It has very few weaknesses but you must realize that Blastoise also has very few weak points (if I remember correctly defenses, HP, Sp. Atk and Atk are all 80+ for Blastoise, with speed being the low point) and is borderline NU right now. Dolphure's 98 base speed is just not enough, its Sp. Atk is nothing too special without Thunderbolt (which it doesn't have), though its defenses are great. If you want to look at a minimaxed starter, why don't you look at Infernape? Broken speed tier, very high attack and sp. atk, uber movepool. Or even Sceptile? 80 Atk, 105 Sp. Atk, 120 Speed, none of its other stats are truly bad.

The trainer also has the advantage of a Potion against Vincent though.