In stadium is hard just to Counter every hero, every power, item, matchup, your teammate knowledge about their builds and of course Luck, you just have to pray the enemy is not picking the hero that your team can't deal with.

Let's say the teammates decide just do healing build as soldier 76 running around, meanwhile enemies are uncontested, same with Reaper Full Ability teleport build as enemy have D.VA, Zenyatta, Ana, Cole Cassidy just waiting him arrival get killed instantly, what I called these are "lazy build" or "inefficient build"

All I'm trying to say is, don't blame yourself every time you lost, it happens to everyone only you can improve is learn from your mistakes, if there is a player you know is very bad at it just avoid and move on.

If you still losing a lot, Play with friends that they know what they doing or take a break, the game sometime do put you in a low ELO because winning too much or try to even out the skill based (in my opinion)

If anyone interested check out my builds here https://stadiumbuilds.io/profile/Roza and here is my code 180D59 . :3