I mean, as far as taking hits, D.Va is pretty bad. But she still can suck bullets in, take a bit of damage, and she practically gets infinite lives assuming you can get away when you're not in the mech and survive.
Yea but... everyone has infinite lives. She just spends her "respawn" time hiding and being mostly useless. And also she sometimes dies and has to wait to respawn normally anyways.
I think you're under estimating D'Va's pistol. That pistol is pretty strong. You can poke at people when you're with your team. I don't know why you'd run off and hide. That just makes you vulnerable to a Genji, Tracer, etc. that is sneaking around the group to get a pick.