I can agree that OpenGl is messy API and takes a lot of work to make games run fast as on DirectX, but it isn't impossible. You run a lot of games not even knowing that they run on OpenGl (since OpenGl is crossplatform) while you are on Windows. Also PlayStations PSGL is based on OpenGl. But where OpenGl fails Linux kernel comes and saves the day since Linux based distributions are much lighter and linux kernel adapts to new things where microsoft doesn't actually care and we actually dont know if they changed anything about their kernel since Windows 98. You can read all Linux changes on this page: http://www.phoronix.com/scan.php?page=search&q=Linux+3.12
Also Direct is the one copying OpenGl since they started Direct by copying whole OpenGl code (since its open-source) and edited it a bit.