I play mag too so sometimes will experience a similar problem.
If you see they're a dk with ≥30k health, don't waste your time with them.
They can't kill you and you can't kill them. They're built that way because that's what they need to stay alive.
True. Just ignore high health tanks and eventually they will evolve to less healthy out of boredom.
Just hit them harder.
No seriously! A few times, I've had problems as the meta changes to deal with tanky players. The common solution seems to be to join them so they can't burst you either - then it depends on either who runs out of resources first or who's allies turn up first..
I sometimes find going the other way can work - forget about sustain and throw that much burst damage into your build that you can still mess up all but the super-tanks. Those you just leave alone.. ofc. you're gambling on being able to kill em before you run out of resources... but hey! can't have everything!