If you're highly technical and no one else touches your machines, then you may be fine.
The claim that no one should use it is trendy right now. The idea that your in-laws Windows box should be left with nothing on it is misguided. But all you do need is to make sure Windows Defender is running and up to date.
The last leg for me was TLS MiTM as an antivirus service. And so I don't use 3rd party antivirus on systems that I care about. I do use active firewalls and connection monitoring though, and I only install software that I've purchased (or open source software) on those systems. Perhaps ironically, I do have antivirus on my old laptop dedicated to watching ahem massage videos.
If you're highly technical and no one else touches your machines, then you may be fine.
The claim that no one should use it is trendy right now. The idea that your in-laws Windows box should be left with nothing on it is misguided. But all you do need is to make sure Windows Defender is running and up to date.