Why can't I live, while others team wipe.

I have been playing awhile now, and admittedly im pretty average. I just play for fun, but I do try to get better. I mostly tank or support as I just fill.

There's one thing I dont understand tho. Why do I always get lit up and melted when I go near the other team, dive or even just walking up but whenever ever someone one is diving my team they live?

Is it a difference in aiming capabilities? Comms? Luck?

Now I dont play magic, but i tried the other night, and was being my sneakyiest, yet consistently died before I even got a dash in, not time to think about getting out. Yet every game other game lately Magik is darn near taking out my whole team. I dont get it.

Theres always a Cap stalling point that my teams cant put down. I play Cap, and barely motion in the direction of point and im dead.

These are just a couple of examples. Im not a delusional DPS thinking my two healers can out out heal 5 ppl worth of damage incoming. I just dont understand why my teams can never kill the one character harassing the backline, while I cant even make it to the back line.

It's gotta be aim right?

Side note/question how is it balanced these dps can kil a tank so quickly, even their ults kill from full health, but they living thru Thing punches, and and Hulk Smash ultimate withOUT heals?