I mean, at the very least, running CAT-6 into every room of your aforementioned apartment and terminating them somewhere sensible with a fiber/cable endpoint wouldn't cost awfully much and would make everything you did here notably easier. Even if it's not used by a given tenant or owner, this stuff like any infrastructure is inherited by the next occupant. Since we got fiber internet, I've not touched a single coaxial line in my home, but when I sell it and move, that cable is still there, ready to be used by whomever buys it. Whether they will or not is obviously their decision to make, but at least this way the option is there. I see no reason why ethernet couldn't work similarly. Every house I've lived in has had a nest of coaxial cable lines in some corner of the basement or other utility area, and most have RJ-11 for phones too.

I would also say that your last note: "a function of knowing what you're doing" does unintentionally I think really well at illustrating the problem. I do not have the slightest clue how plumbing works, but my home came designed from stock with working toilets and showers. I also have a fair bit of knowledge about electricity (enough to change outlets and switches anyway) but not enough to really build out circuits, and my home came designed from stock with appropriately placed (mostly) outlets ready to be used. My point being: people shouldn't have to know how their infrastructure works, and I would argue while a new entry and one that could use some standardization, Internet absolutely belongs in that category.

Additionally, you're using some pretty top-of-the-line consumer electronics there with Ubuquiti APs. I looked into those some years back and to replace my Google Wifi's that I had at the time would've cost me about $1,500, which, I can afford and did consider, but ultimately never pulled the trigger on and I wouldn't be upset in the slightest if Joe Consumer looked at that price tag and had fit, since bottom-shelf wireless routers on the market do the exact same thing (distribute internet OTA) for like, $70.

Now, I don't use bottom shelf personally, I have a mesh network too but mine doesn't allow me to tweak the power of the transmitters nor really do traffic shaping or service prioritization. This is, in my mind, akin to someone saying "there's nothing wrong with the highway, I have a Ferrari and I can get to work in 10 minutes if the cops aren't in the way." No kidding. You've bought one of the best answers to the question at hand, but not everyone can have that. And this is made worse by the fact that there are absolutely tons of shit quality routers built and sold every day that do a bad job of this task, and the only way to avoid that as a customer is knowing a decent amount about network administration so you know what to avoid.

If a home fittings company made faucets that worked as badly as many routers out there do, they'd be sued into oblivion if not fined by the FTC for selling lemon products. I think we need more regulations on Internet-adjacent hardware so customers can have a baseline level of expectation that these things will function at the task they're built to accomplish to at least a certain level of reliability.