Configuring Microsoft Defender Antivirus for non-persistent VDI machines

I just came across this thread and was hoping to get some feedback on an issue we're having with Onboarding our Horizon Instant Clone desktops into Defender.

In a nutshell:

1. We are NOT using a shared intelligence server, we are allowing the desktops to pull down updates directly from WU.
2. We are utilizing a post-sync task on the Horizon pool that runs a script that:
   Clears any onboarding data in place (gold image is clear but we do this anyway)
   Runs the Onboard NonPersistent Powershell

The thing we're running into, is we see a very high utilization number on the disk inside our VMs. Unfortunately, we're unable to trigger this on demand, it seems a bit random. Last night I republished a pool of 700 desktops. It got through the first 480ish no problem, running the task and all, when all of a sudden the remaining ones were not finishing their tasks and they errored out. When I looked into it, the VMs were showing the disk at 100% like this:

Is there a "bottleneck" where X devices onboarding at once can hit a wall? Or are we suffering the consequences of not having the shared intelligence server? We did speak with a Microsoft rep on this, and he led us to believe a shared intelligence box in our environment wasn't necessary. That allowing WU to handle the updates would be sufficient.

Thanks in advance.