I don’t doubt at all that the security threats are real. They have CVE numbers, have been vetted, and no doubt there is exploit code available to test the vulnerabilities and to test that they are fixed (or not) with new drivers.
That Nvidia drivers may be damaging hardware would be another story. I haven’t heard anything about that. It would be a monumental scandal and class action lawsuit, and even criminal behavior if it was ever found Nvidia was intentionally damaging hardware to push sales.
Nvidia has major QC issues in software and hardware but I doubt they are intentionally killing cards. Unintentionally killing cards? Yeah, I could believe that.