Overwatch isn't about who's better 90% of the time in my experience. It's about which team has less of a burden to carry. The system is designed to, if not punish, to not reward extremely good performance. If someone is extremely good at a character it's usually simple to pick that characters counter and, if not shut them down, make their ability to carry more difficult. Versatile characters thrive in these environments.

Picking an easy character not only taxes your personal abilities less but it also makes it easier for your team to work around you. This combined with the fact that easy characters aren't really so inferior to their more skill based counterparts to actually effect the games outcome in any real way.

When you reduce each players ability to impact the game you reduce the value of characters based around individual skill.