Can't remember the details, but MS did drop the ball quite badly not that long ago with Defender. I don't think that makes them worse than most of the competition though, and there is a case that Defender slots into Windows by design whereas the 3rd party AV products claw their way in with horrible hooks that introduce new ways to attack the system.
It is also an interesting thought that the huge performance drain of AV products on things like file open calls to the OS probably make the Meltdown patch not so bad in comparison.