At least with the MacBooks, you do have the option to downgrade back to a previous version of the OS, if you find the performance of the new one not up to par. So why not go back to the version of the OS on your Air that you were once happy with?
For the record, I have the same rMBP 2012 model that the person you're replying to talked about, and it still runs great. But I'm typing this reply to you on a MacBook Air from 2010, running macOS 10.12 Sierra, in Chrome. Still works surprisingly well...
For the record, I have the same rMBP 2012 model that the person you're replying to talked about, and it still runs great. But I'm typing this reply to you on a MacBook Air from 2010, running macOS 10.12 Sierra, in Chrome. Still works surprisingly well...