Her kit is powerful because she’s incredibly vulnerable. Without her matrix, she’s a Hog with more mobility, a lot less danger and zero self sustain. She also has a massive crit hitbox. If your Zen can get a Discord on her, she might as well jump off a cliff because she’s already dead. Her ability to “respawn” is a curse disguised as a blessing. On defense it’s sometimes good, but on attack, it’s almost never worth it for her to stay alive between pushes like Hanamura point 1 because she has to wait for her mech to come back and is incredibly vulnerable while charging it. A mercy can also waste her rez on the Dva because she will always rez as baby Dva.
Meanwhile look at the rest of the tanks. Zarya has one of the objectively strongest kits in the game and it’s not possible to debate that at all,
Roadhog can ensure you are always fighting a 6v5 every single fight and can instakill anyone who isn’t a tank or boosted while providing a massive self sustaining point presence AND an ult that can shred anything unlucky enough to get caught or force them off the point if you use it on Hanamura point 2, for example.
Reinhardt is incredibly dangerous in close range with favorable matches against most of the heroes, an ability to return to the point or instakill a single out of position target and let’s not forget his barrier.
Winston is able to force the enemy to divert their attention, even if he dies which is sometimes enough to win on it’s own and his ult gives him a total of 1500 hp to contest a point with.
Orisa kind of needs a buff badly.
Hammond has control of the battlefield that no other character has. He can make anyone incredibly easy pickings for a widow or open a team up for a shatter, Dva bomb, Deadeye or whatever, can lock an area down for several seconds, force people off of a point or out of a choke, contest some points incredibly well, and just generally be a massive PITA.
With all of that said, the ONLY thing Dva does special that no other tank does directly is use her matrix. Even then, a Zarya can cancel a Dead Eye on 2 heroes or a Dva bomb if your Ana just gets caught with her pants down or whatever. Nerfing her Matrix makes her an ult battery.