Not my experience. I have a 2009 Mac-Mini, 2009 MacBook Pro (just sold a few week ago), and a 2011 27" iMac all running Yosemite and they all run great. Not a single issue. No WiFi or Bluetooth issues nor any discernible lag issues. I also have (2) 2015 13" retina MacBook Pro both running Yosemite that runs great as well. I have read many posts where posters will state that they are having issues with Yosemite and then you have other posters stating that they do not have any issues, both have the same year and model of Mac. Not sure what is causing your issues with Yosemite and I don't doubt that you are experiencing the issues that you say you are having. But to imply that because you have issues everyone will have issues is ridiculous. Have you posted in the forums section about the issues you have and maybe there are others posters that could help resolve the issues you are having? I haven't seen any posts from you in the forums so that is why I ask.
No need to post help: Both devices have had independent hardware tests made and have been erased and reinstalled from the ground up with fresh copies. Mac has been tested with 10.8 and 10.9, runs perfect, but 10.10 is pretty bad. I feel it's just not optimized enough.