Are such soffits common and simply an unavoidable evil that owners of a central controlled residential ventilation system have to live with, or do you consider this poor planning that we should not accept? How is it in your house?
It would be better to have a detailed plan (working plan, execution plan), but it is also possible without one.
In our case, you can see pipes and silencers "surface-mounted" on and under the ceiling of the utility room. In the rest of the house, all elements are located in the ceiling or inside a wall, except for one pipe in the bathroom, where the wall was too thin. If we had a plan, this would have been noticed, and a solution might have been found. Now there is a soffit, which in our bathroom hardly bothers at all (there are other pre-wall installations and soffits anyway). Anyway...
I consider the sketch from your post to be poor planning. Is that the blue ventilation duct? Why are there so many 90° bends? Why aren’t silencers and distributors mounted on the basement ceiling? You can live with that in the basement, right? Then there would be no need for soffits upstairs. I don’t understand the area between the ground floor ceiling and the upper floor floor...