Agree with this. What's more interesting is on the feature level languages do borrow/converge on each other in order to try to secure a position in the market. I note that as an example Java is consdering a .NET like Span feature (https://openjdk.java.net/jeps/412) as an example probably to close the gap w.r.t performance. There are others.

What matters more in all honesty, and what's hard to change IMO is:

- The base of the language (is it verbose, how the base features interact with each other) vs being "tacked on". A language with these features initially. e.g. you mention F# and I know it uses HM type inference, immutability by null, makes null hard to express by default, etc.

- Anything that breaks backwards compatibility (e.g. Java's generic implementation) for example including existing API's. Adding Async afterwards takes time, and changing the underlying model of the language (e.g. Python's GIL, OcAML multithreading) takes time and needs a lot more consideration. Its code, anything can change, its just harder and maybe easier to take something that was designed for that case initially. Being a polygot isn't a bad thing per se I think if it can be justified tech wise.