I also haven't heard of it being outperformed by Java and C#; do you have a source for that claim?
The book iOS and macOS Performance Tuning ( https://www.amazon.com/iOS-macOS-Performance-Tuning-Objectiv... ) has pretty damning benchmarks against Swift versus Objective-C even without using any tricky optimizations (not what you originally asked but something to consider). Of course the whole book (written by a former Apple engineer IIRC) is pretty much full of performance gotchas across many Apple frameworks/APIs, but the chapter on Swift was pretty harsh and basically said Swift fails to live up to its name versus Objective-C (at least at the time the book was written).
I think most people think that Swift performs like Rust/C++/C since it doesn't have a garbage collector and imagine ARC is providing relatively free memory management, but it seems Swift performs closer to languages with a garbage collector due to the various design constraints on the language (interoperability with Objective-C, ARC isn't free, and maybe without the explicit lifetime/ownership declarations in the code like Rust, ARC can't be optimized as well).
Swift is much closer to the metal than .NET, and it has very innovative syntax features. It's more analogous to Rust than to C#. .NET is a strong cross-platform ecosystem, but it's silly to say "we don't need any others because this one's good enough". It's not even the strongest one that currently exists - probably the JVM is. It honestly just sounds like you're hating on Apple for the sake of it.