By a definition that requires you to play a boring, repetitive slot machine. I have a hard time considering that to be a particularly good "definition". Yes, technically you can get anything, but there's something seriously wrong with a piece of gameplay if the best, or only, strategy for playing the game is to play slots for several hours.Anything you can fish up is renewable by definition
In game design, repeatedly killing a player by forcing them to confront obstacles that their characters seem clearly out-matched by is how you communicate to the player "you shouldn't be here; go elsewhere until you can survive". That's how a pseudo-sandbox game tells you when you're in a place you shouldn't be.Pushing your way into areas that are difficult for your current equipment is exactly how you get new equipment that's well ahead of where you are.
This is what makes the Underground Desert contradictory. It is difficult, but the "new equipment" you get there for the most part is not "well ahead of where you are". By the time the area is difficult-but-survivable, you've outgrown the equipment there.
This is not true of pretty much every other area in the game. By the time you can beat Skeletron, you're probably able to survive the dungeon. It may be hard, but it's not "kill you every 20 seconds" hard. And the loot you find there will carry you through the Jungle and much of the Underworld. Something similar is true of the Jungle, just for different builds, classes, and playstyles.
I like the idea of the Underground Desert; it's kind of a pre-EoW/BoC Dungeon. But there's just too much of it, and not enough good within it. Buff some of its stuff, reduce the number of larva and rolling cactii, and it'd be fine.