I used to work for an AV vendor. I'm quite familiar with its internals. I used to look at some C++ and disassembled malware samples. I'm technically skilled for that kind of reverse engineering.
The engine is so lightweight and optimized that other vendors license it.
It's so lightweight that those underspec'd bank ATM machines you use on the streets with the unfortunate Windows XP or earlier will use that AV with nearly zero performance impact.
> AV hogs CPU, RAM, disk, and network resources.
I hear you, but this is not the case with the AV vendor I used to work for. Years after leaving the company, I still pay for my license (at a legacy discount of course).
Actually, one of the reasons I pay for my license is precisely computer performance. Windows Defender has some BS file indexer[0] that clogs the SSD with 100% continued usage. I just dread it. This bug still remains since the days of Windows 7.
Once you get a proper AV product in your computer, Windows Defender steps down. Bug fixed by myself. Done deal.
The other reason is peace of mind: Windows Defender is not a real security product. I know the protection capabilities of the AV product I licensed. I'm not a complete idiot using my computer, and yet, even I prefer to have it installed and paid for.
It triggers me people saying Windows Defender is enough. It's quite irresponsible. People haven't seen half the crap I've seen. Windows Defender is a little weak kitten compared to the beasts' proper AV products are.
I'm not saying buy the one I use. All I ask is that people buy a lightweight one that has been properly tested by an unbiased third party like AVTest or Virus Bulletin (look for their VB100 100% Detection award).
> AV comes with their own exploitable vulnerabilities, often running in kernel mode. AV has their own zero-days and zero-click exploits.)
As Windows Defender does. Remember, if you don't have any AV product, you have Windows Defender.
I feel that you made a moot point, as every software under the sun comes with vulnerabilities (whether zero-day or known).
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[0]: https://nerdschalk.com/how-to-fix-100-disk-usage-issue-on-wi... (read the 15th reason).