"Another thing: the pre-requested leve of aesthetics is just insane. Either I'm missing something, or the game assumes I've got decorations on every single spot and continously increase the size of those, with aesthetical features going into massive sizes just to keep a small block going (or not demoting)."
The aesthetic requirements for common housing development are not extravagant (if you take a look at the attached image you can get an idea of how much space needs to be allocated to gardens, stelae, plazas, mosaics, etc.) Most amenity structures also have at least mildly positive ambience.
You might be tripping up over dirt roads, which have bad ambience? If you replace those with stone and build up gradually using gardeners+ gardens and other lower-tier structures like shrines and alcoves, you shouldn't have too much trouble. Forest and water is considered attractive as well, for what it's worth, though I think swamp is not.
(One thing I should definitely add is a version of the 'ambience' overlay that works off terrain, rather than structures, but I'll have to rewrite the sampling code under the hood for that to work, so that might be a release or two away. I guess having housing complain about specific sources of ugliness might help troubleshooting as well?)
At any rate I do appreciate the feedback- I guess this is all something the tutorial would have to cover!