I'm assuming the drop of first-party support will force me onto a third-party.

I have had bad experiences in the past, so I'm trying to find out if there are any good ones.

I know my CPU will take a hit, but I have cycles to spare despite not having TPU support.

I'm using Nod32 (or whatever Eset calls it these days) for more than a decade and it's mostly not noticeable. I can recommend it over Defender from performance point of view - since I noticed slowdowns on machines where Defender is used. It's hard to know which one protects better, didn't have any kind of "infection" since started using Nod.

Windows introduces vulnerabilities all the time, how is that an argument?

Or do you love the ugly interface of Firewall?

Well, by increasing attack surface you do introduce potentially more vulnerabilities.

And this ain't a fairy tale - lots of stories about AV MITMing traffic, introducing unsecure endpoints, adware, etc.

By increasing the defense surface you do remove existing vulnerabilities. Also disabling Defender is reducting the attack surface