Delusional overconfidence that developer “skill” is all that is needed to overcome the many shortcomings of C is not a solution to the problem of guaranteeing security and safety.
The C programmers I know are certainly not deluded or overconfident. They don't even think "their" language is a perfect one, or even a very good one. They just avoid black-and-white thinking. They take a practical approach about memory issues, seeing them more like any other kind of bug. It's a different aesthetics than you would maybe see from many Rust folks. They want to be productive and want to be in control and want to understand what their code does. In turn, they accept that in some cases, bugs (possibly memory bugs) creep in, some of which could go unnoticed for some time. They tend to not see that as a huge issue, at least in general, because an issue that has gone unnoticed (or didn't manifest) is often less of a problem than one that is immediately obvious. (In case of data corruption, it _can_ be a huge issue, and you have to add safeguards to prevent it, and have to be accepting some residual risk).
They understand that everything is a trade off and that with experience and practice, good architecture, good tooling etc. you can prevent many bugs early, and detect them early. They have tried many approaches to prevent bugs, including fancy languages and constructs, and have concluded that in many cases, perfect safety is not possible, in particular it's not possible without seriously hurting other requirements, such as productivity.
As to valgrind, I can say that it was a bit of a mixed bag for me. It did help me finding bugs a number of times, but I also had to configure it a bit because it was producing a lot of noise for some external libraries (such as libc). I don't really understand the underlying issues.
Btw. kindly look at the other issue that I overconfidently waved away as "probably a false positive"?