Yeah you're probably right. The problem with multiplayer games is that people are selfish

This is not a problem and it does not hold designers back. It is inevitable that every game which is played with a team will give players who coordinate with each other a huge advantage over an unorganized team. However some developers like Blizzard love to artificially force "teamwork" on everyone by making sure little Timmy who picks Mercy and holds LMB is given equal value to that of your sweaty Widowmaker who has to practice his hand-eye coordination and reflexes, or in case of HotS build the whole game around linking everyone's power level to a single progression bar.

You could also see traces of this design philosophy in Battlefield 5 with the changes to spotting, ammo and health.