I think the best way to think about such things is in terms of niches and ecosystem. The niche of functional and native is small and already well served by Haskell, Ocaml and even Rust to an extent.

The .net, python and JVM contain some of the largest ecosystems. Even if small relative to C#, the niche size and health of a functional language on .NET is much larger than if it were another native langauge. Speed, documentation and tooling might not exactly match C#, but are excellent in comparison to other functional languages.

In a similar vein, niche size for a transpiled functional language is much larger, more so if the language prioritizes playing well with its parent ecosystem. There is room enough for Fable, Clojurescript, elm, purescript and Reason to co-exist.