Well, it is hindsight 20/20... But also, it's a lesson many people have already learned. There's a reason people use canary deployments lol. Learning from other people's failures is important. So I agree, they should've seen the possibility.
I saw one rumor where they uploaded a gibberish file for some reason. In another, there was a Windows update that shipped just before they uploaded their well-tested update. The first is easy to avoid with a checksum. The second...I'm not sure...maybe only allow the installation if the windows update versions match (checksum again) :D
The kernel driver should have parsed the update, or at a minimum it should have validated a signature, before trying to load it.
There should not have been a mechanism to bypass Microsoft's certification.
Microsoft should never have certified and signed a kernel driver that loads code without any kind signature verification, probably not at all.
Many people say Microsoft are not at fault here, but I believe they share the blame, they are responsible when they actually certify the kernel drivers that get shipped to customers.