Rust is a tool not for application development. It has a huge space in drivers, renderers and other low level places.

Node and Python are dynamically typed and at least originally scripting focused. They are not the right choice for many development active which are focused.

.NET plays with Go and Java in the same category of use cases. And there it boils down to devs you have.

Regards ecosystem: I am at home in both, .NET and JavaScript (browser more) and I can tell you: ecosystem is in 2025 no problem. Was back in the 2010s.

About the devs: you have what you have and hire along. Like Java, it will not go away. You get good ones and bad ones. Like for any other language.

Let us be less religious here. Objectively, .NET is like Go and Java a fit contender for its niche and selection goes along the lines what you have as workforce/systems already in place. In a startup situation you follow the preferences of your CTO.