In the Netherlands the base Golf starts at €27k. When you customise that to the trim you get stock on the id3 st/plus (st little less, plus more advanced extras) you get to €42382 (config code 8N1B7B) which is not that different from the €43k for the ST and €44k for the Plus.

I can imagine that the Golf being known tech will have a larger profit margin indeed. In the other hand, most of the extras in the id3 are shared technology anyways.