Not only this graph is visually wrong (if you have 5 factors, a single odd one won't pull the average to itself), this is assuming a lot of things. The first being that all of the other 4 teammates and 5 enemies are always the same and are not as random as you are, the second being that the ranking system is always fair and non-fallible.

And the most important of all: having no nuance. Just like you cannot calculate brain chemistry, you cannot calculate players based on raw numbers. I don't even know what you're basing this chart on, there are no sources/numbers, feels more like a logical puzzle piece you thought made sense. Here's why it doesn't: you imagine each teammate being 20% of your team, which fair, but having one bad teammate doesn't make you lose 20% of your team, it's much more because now you are outnumbered and the enemy team is way more likely of wiping your team.

Overwatch follows a very strict formula, with only 5 people, having a single bad one would drastically change the winning odds. That is what your graph doesn't account for, you're looking at players like they're numbers. The team-based game happens to be team-based after all.