I've had a few houses throughout the lifespan of this game so far. Couple larges, couple mediums, with a sprinkle of smalls. As an end-game PvE player I've hopped servers a few times related to groups that I've integrated with. I've usually kept up with house discords, because I like the convenience of a house, and even more so I like having a house just to have one, like owning a luxury watch.
Now on to the problem at hand. There is WAY too much money in this game, especially involving the housing moggles. While I can't say if there should be adjustments to FC housing even though there are more people in an FC, but I don't want to hamper community growth. For personal housing the cost for most are way off and should reflect more on it's finite quantity and the actual rarity. No reason a mount should sell for the same price as a large house. There are a few things that could occur here to help this scenario. A lot of people will argue against this, mostly because as most people know, everyone is trying to game the system to their own profit.
First scenario: House cost to reflect their true market value, or pretty much what players are going to bid for personal housing prior to the lottery for a relo.
Smalls: 25-50 million
Mediums: 150-250 million
Larges: 500+ Million
Again, people will hate but let's be honest...this system and these costs have been around for the last 2 years, and it's pretty much worked, and we just delt with the fact we were probably funding RMT, as they botted for houses. In this system cost hasn't changed from what people would pay, but fundamentally removed massive amounts of money from the game.
Under this system, players can be give the option to sell their home at the market cap. So for a large @ 500 million, however that player will only receive X% back. So let's say FFXIV housing commission takes ~25%, house sells for 500 million, player recoups 375 million. Selling a house in this case isn't about making a profit, it's about said player wanting to move house, transfer servers, make some money back on an investment they don't want anymore.
Houses can still devalue over time up to whatever some arbitrary fair number would be. Let's be honest, most houses will never devalue and people will be on it fast, but if say on new servers, smaller servers, some houses will come down before being bought, maybe up to 50% off. In this small window a player on these servers actually might make a profit, but this is a really narrow window of possibility.
tl;dr: Current systems for housing whether FCFS/Relo or Lottery are terrible systems of RNG with more holes in it than swiss cheese, that people are taking advantage of for personal gain. The root problem is the value of houses are not being reflected in these systems when the actual player based value is so much higher.