He's main flaws are that he can be a bit turnover prone, and that he doesn't have a standout jump shot.
That said his AST:TO ratio is close to 2 which is perfectly fine for an NBA PG, and his jumper is better then advertised (he shot 37% from three this year, even if his attempts werent that high).
Outside of his turnover rate and his jumpshot (both of which should be improvable) he doesn't really have any other flaws.
He's basically an elite athlete, elite defender, a borderline elite passer, an outstanding rebounder (for a guard), is an elite slasher, and has a very good midrange game.
Hard guy to fault really. Hes basically a more athletic Marcus Smart with a better jump shot, better ball handling skills and better passing instincts. Or he's D-Wade with better PG skills.
Getting Dunn pretty makes Smart 100% redundant.