If you ran a speedtest, this only tests speed, not quality. Otherwise, if you ran a WinMTR, please post the results here. And if you haven’t yet, please do so we can try to figure out your connection issue.
https://us.battle.net/support/en/article/27780
More information on why this is only affecting Overwatch and not other services: Common Technical Issues and Solutions - #23 by Drakuloth