Focus stealing has been an issue in windowed multi-tasking environments from the beginning. It's certainly been an issue in all macOS/OS X versions I've used since I started in 2011.
I've been using windowed multi-tasking environments since 1986. Never been a problem for me (SunOS -> Solaris -> Linux). I rely very, very, very much on focus-follows-mouse.
I've been using windowed multi-tasking environments since 1986. Never been a problem for me (SunOS -> Solaris -> Linux). I rely very, very, very much on focus-follows-mouse.