My biggest gripe with JetBrains' lineup is the different "spins" for different languages. They should make a single IDE with plugins for many different languages to deliver a vastly superior experience to VSCode.
Multi-language code bases aren't that uncommon either. As you say mixing C and Rust is common in apps and systems level programming. Mixing JavaScript, TypeScript, Go, and other languages like Python is also pretty common in web-centric stuff.