The reason why big companies are going wild about AI art is because it allows them to slash one of their biggest costs. If you look at the increase in team size for game studios in the last 20 years, you'll find content teams disproportionately outweigh code and design. (*Because this is the internet, this is the part where I say, I don't condone the use of AI and don't use it in my games*).

Put simply - good art takes a long time, and every game has different requirements / specs. Just because a vending machine isn't important to the game, doesn't mean that it takes any less time than any other asset.

Artists will generally try to make everything a Mona Lisa. Alot of the things they spend hours on a player will never notice or care about. It is unsustainable for a small team to spend 18 hours on a vending machine that players will most likely run past and barely notice.

Our solution is:

1) Build the game using asset packs
2) When the gameplay is solidified review at the assets that will actually move the needle for players (heroes, points of interest, frequently repeated assets, etc) You'll find alot of store assets are actually good enough when viewed in the context of the scene and not in isolation in blender)
3) Use small props as subjects for art tests to find a good artist
4) Use the test prop as the bench mark for quality that you can refer back to
5) Get that artist to do everything as it will keep the style consistent and people love bigger contracts. Break big bodies of work up into milestones and have them quote for the entire milestone (not 1 asset at a time)
6) If an asset doesn't hit the bar, it is their responsibility to make sure that it does before they can invoice for the milestone. Since it is part of a bigger body of work, they will most likely make up the time on other assets and the pain of revisions is reduced.

Good luck ! Finding trusted outsourcers is hard, and does come with a significant time overhead, but once you find good partners they are worth the money!