I got a new laptop from work recently and I didn't spend a great deal of time looking it over as i was busy and ... of course I hit some random performance problems as McAfee was abusing my machine while I was trying to work. Endlessly installing antivirus programs is getting pretty old.

All AV software has the desire to not negatively impact performance because if it's horribly slow people will uninstall it / quit paying for it.

The parent comment is pointing out that companies which primarily produce AV products benefit from the continued existence and fear of malware (to a degree at least). This is different for MS, as the eradication of Windows viruses will help Windows, which should be large enough a benefit to override any perverse incentives Windows Defender would otherwise have.

I know what you're trying to say is "also, Windows Defender isn't as slow", which happens to be true, but I think that's simply an emergent effect of other factors, such as AV companies feeling the need to "do more" to add value (whereas Windows Defender is funded by MS, so it has less incentive to "stand out").