But are there any DEs that make use of this and include setting screen brightness on external screens as easy as for laptops? Is it because each screen manufacturer implements altering brightness/contrast/etc. via ddcci differently?

Sounds great, and is very welcome! Please merge. Thank you. Do you guys have any idea why ddc/ci controls for brightness control of external screens are not yet implemented in any major De? It's the same on windows, still not part of the Os. Third party tools available since ages.