Apparent contradiction about IJSInProcessRuntime?

[user72356]

According to https://docs.microsoft.com/en-us/aspnet/core/blazor/webassembly-performance-best-practices?view=aspnetcore-5.0#consider-making-synchronous-calls, webassembly-only apps can optimize performance by casting IJSRuntime to IJSInProcessRuntime.

I've been using this technique successfully when calling JS functions, but recently when trying the new JS isolation feature, I saw this comment from Steve Sanderson: #28627 (comment)

JavaScript's invoke mechanism is inherently asynchronous - it always returns a Promise - so it's not useful to call it synchronously in this way.

So if invoke is asynchronous and always returns a promise... What's the point of IJSInProcessRuntime?

I might be confused about what Steve calls "Javascript's invoke". Is this different than .NET's IJSInProcessRuntime.Invoke?

In other words, IJSInProcessRuntime.Invoke is going to run synchronously against a regular JS function, but will return a JS promise when run against an import statement?