Usually the main message is that they haven't thought about the organisation of their datastructures sufficiently. In my experience this is also very important

Usually the main message is that they haven't thought about the organisation of their datastructures sufficiently. In my experience this is also very important with a GC, but you don't get much help from the compiler, instead you wind up chasing strange issues at runtime because object lifetimes don't match what you expected (not to mention, object lifetime is more than just memory allocation, and GC languages tend to have less effective means of managing lifetimes tightly). I agree async Rust is very painful still. It's very much something I don't use unless I have to, and when I do I keep things very simple. (Also, the lack of a package manager for C is much more due to historical cruft around build systems than it is difficulty getting C libraries to work together. Most of them can interoperate perfectly well, though there is a lot more faff with memory book-keeping)