I played Mauga against Orisa in some games. It felt like she could be mowed down quite easily if she didn’t have Javelins up. Her Fortify is NOT immune to burning effects from ‘Gunny’ (Incendiary chaingun), thus the critical damage from ‘Cha Cha’ (Volatile chaingun) as well.
Simultaneously firing both chainguns severely lowers the accuracy, but it doesn’t matter if she’s close and her hitbox is massive enough to be hit by most bullets. When Orisa rushed into my team and started ulting, I just fired everything at point blank range and she’s done shortly after.
In mid range fights, I only fired Incendiary chaingun at her for better accuracy and she’s quite easy to be ignited due to large hitbox. When she’s ignited, I only fired Volatile chaingun for crits.
What? I found it really easy to kill him with Orisa, you can keep him at range and he doesn’t do much damage to orisa, her ult could be used to counter his? I’m not sure if he can mow you down before you can charge up though but he needs a lot of focus healing to be able to win against an orisa from what I saw. He doesn’t really do much damage from mid range either and you can push him of.