>I don't understand your comment about reference counting being intrusive.

It's intrusive because you can never really stop thinking about it if you want to write correct code. Here's an example from a very interesting article by Mark Sands [1]:

How quickly can you tell whether or not this piece of code has a reference cycle?

    class ServiceLayer {
        // ...
        private var task: URLSessionDataTask?

        func foo(url: URL) {
            task = URLSession.shared.dataTask(with: url) { data, response, error in
                let result = // process data
                DispatchQueue.main.async { [weak self] in
                    self?.handleResult(result)
                }
            }
            task?.resume()
        }

        deinit {
            task?.cancel()
        }
    }

In my view, reference counting does not combine very well with heavy use of closures.

[1] This is an interesting read: http://marksands.github.io/2018/05/15/an-exhaustive-look-at-...