CapnZapp
Legend
Just to dispel a misconception (not to say "blatant falsehood"):Other than organized play, which has item regulation ostensibly as a method of balancing various tiers of play (with hit-and-miss success IMHO), I don't see any implied bad-wrong-fun implication. The models provided by WotC are suggestions that go along with their idea of bounded accuracy assumptions, ie magic is not essential to characters as they level. That's a base case, which they cater to, but in any home game the sky is the limit and has some level of support, especially with the release of XGtE.
Nothing forces you to use those systems in your home campaign, either, other than the collective echo chamber found on the internet which tends to be conformist so to avoid groupthink criticism (again IMHO).
There is zero support for anything like a magic item economy as the ones supported the last twenty years or so.
The only value of the 5E rules for downtime and magic buy/sell is to be able to say "we do have something". Unfortunately, your post is proving that those rules provide a smokescreen that fools too many people.
Since it is all based on rarity, it is utterly useless for any campaign that hands out gold instead of magic items, so that the players can choose themselves what they want to buy.
The reason for the fan-effort "Sane Magic Prices" is exactly that the WotC support is entirely random... or as they would say: insane. Winged Boots more rare/expensive than the Broom of Flying? Weapon of Warning uncommon while Vicious Weapon rare?
Are they mad? A Weapon of Warning is a hundred times more valuable than a Vicious Weapon. (171 times more, in Sane's opinion)
So please don't tell us WotC is providing "some level of support". You aim to speak for us, but we do not want you as our spokesperson.
The first step in providing what you need for an utility-based economy is to tear out everything WotC as written so far, especially the faff in XGE.
Then... there is no step 2.
We're still waiting for step 2.
Thank you.