I have the same thoughts too about the Action button. As a runner, I find double tapping the screen to mark laps a very inaccurate method. Very often, if not every time I try to double tap the screen to mark a lap, the Watch doesn't register it or it results in the Watch displaying the next screen. It's really terrible.
But then I think: is the addition of a button worth the difference between a Series 8 and Ultra? That's a $400 difference with the Ultra being twice as expensive as the model of Series 8 that I would get. SMH.