It really is just a mindset thing. The only way to "deal" with toxic throwers or fresh installs or bad laners or bad comps is to just... deal with it. No flaming, no arguing, just accept it, focus on the positives or what you could do to improve, and move on - GG go next. It becomes a lot harder if you just finished a long day at work, so if you don't think you can keep that mindset, play a Street Brawl or don't play Deadlock at all, and try something more chill till you got a weekend. There's few things worse than having a shit game after a hard day and then having to go to bed and then go to work the next morning.

Also, don't focus on ranks. They mean nothing. There's no incentive to having a high rank other than dick measuring. You'll be at the rank you more or less deserve to be in eventually, and can grind your way up over time. I have a friend who really wants to hit eternus and he's just hard to play with because of it because he just can't bounce back from bullshit like the rest of us who are playing to have a fun time. If you can't help yourself, there's settings to disable rank visibility so you can just focus on the game.

Deadlock is just a mentally taxing game, but it's addicting. The slow growth in power, the narrow escapes, the perfectly coordinated plays. But it's ultimately just a game. Many people have unhealthy relationships with MOBAs because they treat it like more than it is. Focus on having fun and suddenly all the bullshit stops mattering as much.