It is as you say, I have made a feature request for this:
However, with Cubase 14, there has been some improvement. If you use the new Score Editor and insert any tempo there, for example Dotted Quarter note = 60, you will see that this action will have an effect on the tempo track. It will change the tempo to 90 so that what you have written in the score sounds as it should. The parts (sheet music) will also have the correct tempo number on them (Dotted quarter = 60). The only exception would be the number in the tempo track window, and down in the Transport Panel, which will still read Quarter = 90.
Not completely perfect yet, but using the Score Editor of Cubase 14 really helps with this issue. Try it, even if you don’t really intend to hand out parts to musicians.