Don't let yourself get seen. You can know if you're seen because a red eye pops up next to the map on your screen. You can't be targeted by them if you can't be seen. It doesn't matter if you're exposed for a little bit, often the user needs more time to react. You can reduce your exposure time by rushing between positions(drag the d-pad forward far enough and all mechs can rush for a limited time before going cooldown). Use a fast mech. You can see without being seen by standing close to a wall a bit away from the corner and rotating your camera to face away from it https://9apps.ooo/. This way you can tell what is coming your way and know if you might be seen. As you move from position to position being seen as little as possible, if at all, you can effectively get within range of the rocket mortars user and neutralize them. This is often their best build and they stink otherwise so they get mad.