Code auditors are a crapshoot. I worked around financial auditors and they were much more consistent but thats likely because standards are more well defined.
If you get a good auditor they can find a ton, but most are box checkers there to make the audit company as much money as possible.
Quite possible. Ours were good, they just didn't benefit from LLM superpowers back then.
After my Mythos experience, I was wondering if there is really still a market for human code audits. I guess yes, but the work will be different, just like coding (and marketing and so on...) is different now. You still need to have an expert to wield the new powerful tools.