You know my secret to making players not quit on me? Deliberating making my Mech not as strong as it could be. Reducing my hp from 2000+ to 1666 especially, but also not using all Mythic weapons.
Why does this make people not quit on me? Because they go into the fight with a fair chance and actual possibility to win, so they play it out.
Sure it means I auto lose against mythic, especially full mythic, Mechs, but oh well I just quit on them the same way someone rank 2 or low rank 1 still using epics instant quits on me. But that's a small price to pay, because that mythic/full mythic portion of players is such a tiny percentage of the player base, and there are loads more players who aren't even using 1 mythic.
So I'll say it again, if you want people to stop instant quitting, level the playing field. No one instant quits when they have a fair change or an advantage, they quit when they have zero hope.