UPDATE: On the second inspection, making CowType Equatable does not fix the issue. On the Swift.org forum, Jonathan Hise Kaldma thought that making CowType Equatable might solve the problem. It was a good thought, but didn't work out in this case.

As @OOPer indicated, using an object is a way around the problem: I needed to use this to avoid the expensive copies. swift final class Container: ObservableObject { private var cow = CowType() var values: [Int] { cow.values } func append(_ value: Int) { objectWillChange.send() cow.append(value) } } Interestingly, @Published runs into the same problem as @State, making a copy at every iteration. e.g., swift final class Container: ObservableObject {   @Published var cow = CowType() } This makes cow make a copy every time it is mutated.

I think you can async let to kick off the tasks and then await a tuple of results.

Your LineMark is missing series. I think if you put that in it will break it into multiple plots like you want.