At the rate of loss, I'm sorry, but you're just wrong.
Let's pretend you had a strong friend that was your rock. Whenever you had a problem - they were there to settle you. Well, now, not only have you lost due to Thanos, but so have they. When your rock becomes a roll of toilet paper, what do you do? What about their "rock"?
It's a domino effect, and it would take longer than 5 years for the world to return to some form of normalcy after losing 3.5+ billion people.
My point was that Barton is a particularly 'strong' character - mentally and emotionally - and he resorted to becoming a murdering vigilante. That's what happened to a strong character in the MCU.
There's also no storytelling logic for the writers or directors to make out the Earth to be a paradise after genocide. They made a writing choice that Thanos is "right" with their dialogue about Gamora's home in Infinity War. They were making the opposite point about The Avengers being right in Endgame.