@simonmoon I don’t know about the mastering process, but my recent experience with entry level gear may provide some insight. In the last 4 years, I started with KEF Q150 stand mounts on Monoprice Monolith stands. I didn’t know it at the time, but my soundstage and imagining was limited to a line between the tweeters--a 1 dimensional soundstage. I replaced the KEF’s with B&W CM9S2 towers. The line of a soundstage expanded to a wall, which was only 2 dimensional, being height and width. More recently, that wall gained some depth when I upgraded the streamer to the iFi Zen Stream.
Two channel mastering is likely very different from the object placement afforded by the new spacial audio music mastering. But I would argue that there is some way in which soundstage height does exist. I would guess that someone who argues that soundstage height doens’t exist is probably proceeding from a set of definitions from the spacial audio world. Probably just a definitional problem where people are talking past each other.