Sorry, sleepless night. I'll doze off after this.>>423404
"I do mind the gameplay impact they have. And the non-wall options are either poorly coded or there is some bug (using the GitHub version) which means the only reliable way to go up is building walls."
The city here was built up to maximum housing levels on the "dangerous" Hueypochtlan map, using alpha build v0.5, which should be on github. Some walls were built, but they only enclosed a small portion of the settlement.https://twitter.com/PerspectiveGam6/status/1362125170169757702
If you take a look at the danger-map overlay (under the military tab, screen attached) you should get a display of which areas of the map are perceived as relatively safe or dangerous, but I'm fairly sure that building enough barracks/fortresses/hunter-lodges and putting housing close to the map's centre should increase your citizens' feelings of safety.
"Speaking about housing upgrades: there is gorillion of conditions to go just a notch up, with no spread to them. Is the reasoning again historical, or there is some gameplay aspect to it?"
The pre-requisites for housing evolution are not dissimilar to what you'd find in the Impressions series (entertainment, health, nutrition, different goods, safety, etc.), but there are somewhat fewer tiers of housing. I guess that accounts for the lack of 'spread'? (I don't really have the time/budget to do a bajillion different housing variants, I guess is the main reason?)