Firstly if your team goes mass dps like that, my suggestion is you have to have to just ignore this and play your best with a self sustaining hero, so someone that self heals or big shields like rein, mei, hog, and just play your best.
Still try and work with your team to see if you can make it work, but ultimately the attitude of your team mates will suggest that they’re not going to come back and save you as a healer, and you won’t get any heals to be a proper tank, so just go it solo.
2nd Unless you are 100% sure you can play a hero, NEVER fill. at least below 3000, don’t waste your time.
The bare minimum, have 1 hero from each class that you can confidently play and just go with those. I play Pharah, Mercy and Orisa, and that’s it.
If you want a healer, I’ll play mercy, if you want a tank, Orisa’s what you’re getting. Why?
Because SR gains and losses below 3000 are performance based. 4 Scenarios
You win - you play your best hero, you do great - good SR gains
You win, you play a fill hero, you have bad stats and were carried - bad SR gains
You lose - you play your best hero, you still do great - small SR loss
You lose, you play a fill hero, you have bad stats - BIG SR loss
I can explain further about Performance based SR if you don’t understand that concept.
Here’s what you do
If your team plays like a team, you join them
If your team plays like they’re playing solo games, you play solo your self and just play your best.
You can’t win them all, but make each game about improving and learning your own game, rather than what your team did, as you have 0 control over that.