HN user
What do you find insane about the C# `List` source code?
I'm not a C# programmer, but the public API looks sound, and the entire thing is like 1K LOC including docstrings (I guess the inherited code would add to that).
I think the point is that these data structures can be the foundation of a pure-functional style of programming.
You wouldn't drop these into an ecosystem where the programmers are used to dealing with mutable structures.
Now, whether using a purely functional language correlates with writing less bugs is a separate discussion, not sure what the modern consensus is.
I think TCO and JVM are orthogonal discussions -- by the time the bytecode is generated, the TCO may have already been performed.