What measure are you using to determine the performance is terrible? As a developer, I have always had issues with Antivirus. If your compile times are crap then AV should be one of the first things you try disabling.

Hell, I've had overly aggressive AV (McAfee) locking files in temp data folders causing performance to falter in running applications (Visual Studio, Pidgin, Outlook, Office).

Why does the end user care about compile times?

I've had the same experience, I've just taken to whitelisting all of the cache, assembly, and lib folders throughout the workflow (and processes).

Never found an AV which didn't seriously hamper build times, since building often involves a lot of process start/stops and new small files, both of which are kryptonite to AV.

MalwareBytes Enterprise recently got completely uninstalled as it was locking random files during compilation indefinitely. They have a fix but only for the consumer branch.

Yes, you can disable anti-virus per directory or per-process.

AFAIK. Certainly for some anti-virus software.

Do you have any numbers from other products to show this is an issue with Windows Defender's performance, and not just with the general concept of scan-on-access antivirus?

You can exclude bin directories from Defender: https://support.microsoft.com/en-us/help/4028485/windows-10-...

I wonder if their anti-virus also delays the start of their Edge browser.