MS Professional support for Defender ATP is nonexistent

TJ Cornish I feel your pain.  In the last few months, I've had a few "Professional" MS Support cases open to the tune of $499 a pop and they've all turned out to be a joke.  The experience is anything but professional.  Fortunately(?), it's not just Defender ATP where this backlog exists, it's "Professional" support across all of their products as far as I can tell.  My most recent Defender ATP support case was opened on 4/3 with Severity A (expected response 2 hours) and after multiple followup calls initiated on my end, I finally heard from Microsoft on 4/16.  It's also impossible to really chase anyone down since the don't let (or claim not to let) the individuals opening the cases have any direct contact with the teams providing support.  It's now 5/6, and this case still had no real movement.  They haven't even verified that the issue is reproducible even though it 100% is (e.g. Chrome win32k SysCalls being blocked regardless of any mitigation rule exceptions).

You may not know this depending on your organization's size, but there is a level of support above "Professional" which doesn't operate on a pay-per-incident (PPI) basis, but rather bills hourly.  This is the only level that Microsoft very clearly takes seriously and it is known as Premier support.  However, if you're a smaller organization, you literally cannot access this level of support without going through a third-party that has a contract with Microsoft.  Then you get the luxury of paying the third-party their hourly rate to manage the case as well as hourly rates to Microsoft for their work on the case, but at least you will finally be dealing with a responsive individual.

Anyway, you're not alone in your support struggles.  It's infuriating.  If it's any consolation, you can typically get your $499 refunded when these cases go nowhere.