My admittedly biased view from the other side of the fence is that it may be a lot (little) quicker initially but you run up against code quality/maintainability and performance struggles far sooner.
Granted in a startup worrying about next week is wasted cycles but I don't think rails is so much more productive as to justify switching away from an existing stack (whether Laravel, Django, .NET or whatever. While Rails was a paradigm shift when it was new most all other languages and frameworks have adopted large amounts of the lessons from Rails). I'd urge you to give C# a second chance
Granted in a startup worrying about next week is wasted cycles but I don't think rails is so much more productive as to justify switching away from an existing stack (whether Laravel, Django, .NET or whatever. While Rails was a paradigm shift when it was new most all other languages and frameworks have adopted large amounts of the lessons from Rails). I'd urge you to give C# a second chance