Why do you think Swift would be the best language? I am doing a lot of C#, and so far have not seen anything in Swift, that would make it feel better. In fact, at this moment even Java is doing leaps forward, so will quickly catch up on syntax.
And C# and Java have a benefit of JIT VM by default, meaning you only build once for all platforms, unless you need AOT for whatever rare reason (which they also have).
I'd say the culture is very, very different. Java/C#-heads are in love with OOP and create layers on layers everywhere, hiding as much state and methods as they can (you can't use this operator, you'll shoot yourself in the foot!) and rarely doing pure functions. It's just a long way from how math works.
Not saying it wouldn't work, it definitely would, but I think I'd rather switch profession than deal with Maven and Eclipse in 2020.
Swift culture is more about having non-mutable structs that in turn is extended via extensions and heavy use of copy on write when mutable structs are needed. It's a small difference but it's there.
I fail to see how culture is related to the language.
You have a weird notion of mutable by default in either Java or .NET. The former is notorious for builder patter because of that exact reason. Does Swift have special syntax for copy + update like F#: { someStruct with X = 10 }?
Never had problems with Maven. How is Swift different?
People have not been using Eclipse much for a while. There is IntelliJ IDEA for Java and Resharper for C#.
I might be wrong but as I've understood it Builder Pattern is mostly used as a solution to mitigate mutable state from being accidentally shared. Which is duct taping around the complexity instead of removing it.
I don't really know why but the coding patterns (what I call culture) that are popular for each language are very, very different even when they can support the same feature-set.
My understanding is C#'s behavior around structs is identical, except it is not called "copy-on-write". From what I see this behavior is identical to copy-always from language spec standpoint of view. If an actual copy is created is down to the code generator, but semantics is the same.
And C# and Java have a benefit of JIT VM by default, meaning you only build once for all platforms, unless you need AOT for whatever rare reason (which they also have).