The whole point of Fil-C is that it is fast enough to consider using in production for some applications while still guaranteeing memory safety. We already have ASAN and Valgrind and other tools for development purposes, that's not what Fil-C is targeting.
So Fil-C is competing with Go, C#, typescript and Python. If I’m writing a greenfield project where “bare metal” performance isn’t needed, why would anyone choose Fil-C over a more mature GC language?
C is more verbose and more error prone than Go and C#. It has worse tooling. It’s missing decades of language features. C isn’t properly cross platform. There’s no package manager. The “standard library” isn’t fully standard. It’s full of sharp edges and bad decisions.
I can imagine using Fil-C to run legacy code. But for new projects, it just seems worse in every way compared to Go, C#, typescript and friends. It’s worse, slow, and inconvenient.
Of the group of languages presented, your argument has more merit for Go. With C# and others, there is an additional OOP argument in there, that splits into different factions.
But what is being overlooked, is the massive numerical dominance of C programmers and projects, along with legacy and embedded code. There is going to be a preference for writing and using C, that could arguably fuel Fil-C for a very long time.
I am assuming that Fil-C introduces orders of magnitude less overhead than ASAN or Valgrind.
Also, it’s probably fast enough for apps to be deployed in something like a staging environment for integration tests to run against them. Production deploy/release can then happen using a tagged version that gets compiled using vanilla GCC/Clang.
I'm not sure about the speed of ASAN, it may be comparable but doesn't guarantee memory safety. It's only for catching mistakes and not secure against an adversary. Valgrind is dramatically slower.