[artsrc]

Handling concurrency should be an accepted part of the skill set of GUI development.

Writing a user interface that can respond to user input, whilst also being able to handle and respond to a long running data access or computational requests is a concurrent problem.

Having a single threaded model with callbacks, like the JavaScript browser model is one of the less complex ways to handle this.

I agree that a less complex model is appropriate for some developers/applications. But to call yourself a "skilled-professional GUI-developer", you need to get awesomely brilliant enough to handle this.