D'va can't shoot while using her defense matrix (shooting is the same button as canceling). Bastion is a weak counter to D'va, except when she ults.
She doesn't need to. She can boost while using defense matrix, so you hit it, fly into his face, and then kill him at point-blank range. He doesn't do as much damage as she does point blank.
This is simply incorrect, bastion does ~450 dps at close range, D.va does ~170 dps (if all pellets hit) at close range. It's not even close.
I've been on both receiving and shooting end of the bastion gun, and the defensive matrix doesn't really help because bastion is very good at shredding D.va :/ I don't know if boostering into bastion unseiges him, which if it does would make D.va ok against bastion.
Almost everyone is good at shredding D.va because the whole front of her mech (the part where she sits) is her weak point, so it's incredibly easy to get critical hits on her. I actually found I did better in "fragile korean girl" mode because she's faster, harder to hit, and her critical hit point is much smaller. Her pistol is surprisingly powerful too.
It's very useful to have a Roadhog chain a Bastion before you boost up and rain justice from above with Pharah. Also, funfact, Roadhog's chain is hitscan, which means you don't need to lead your target with it. I just found this out today.
Just googled it and you're right! it's hitscan, but with a travel time. If they are under the crosshair when you press the button, they will get hooked when the hook reaches them even if they go behind a wall or something because only the initial hitscan button press matters.
...which explains why I'd miss so many hooks since I was trying to lead it.