I am running 10.10.3 on a 2011 iMac and Yosemite runs great on it. No UI lag and no WiFi issues. Not sure what issues you were having running Yosemite on your 2011 iMac.
He must be a ridiculously unlucky guy and gets every Apple devices with problems. If we measure that from the quantity of Apple hate he is spreading on all his posts...