Edit: Sneak, H64 is less ban worthy than delfino. No walk-offs or water. What is your thinking man?
That... just isn't true.
Hyrule Castle is a stage with permanent walls and is an overly large stage for 1v1 matches, allowing faster characters to avoid their opponent easily. Because of the layout, camping is also prominent issue. In fact...
It's just recently been banned in 64 at Apex 2014. It's important to note that the original 64 version had a dangerous hazard, though that was NOT a singular reason for its ban, but it did contribute towards it (stalling and camping as well). Back to Minus; we have no outright "hazard", so this should be more viable, right? That would be true if it wasn't for one thing; infinites. It's possible to perform truly inescapable combos against the walls with our physics (a good example attack would be Fox's shine).
Delfino on the other hand, has been shown to be a competitively viable stage throughout Brawl's lifetime, occasionally seeing "starter" status in some lists. It has been banned in more conservative rulesets, but not for the points you're making (MK does so well there, and not many TOs wanted to buff his CP options). Now, it's true that portions of this stage have no "offstage", just floor. However, before we cry "BANNED", let's investigate it a little more closely. Why do we ban walk-offs? It's not because there's no offstage bit, it's because they can be abused in a way that "marginalizes player skill".
sunshade (via SWF) said:
In a walkoff's example, a player can simply camp at the edge of the screen, sheildgrab, and throw backwards to score extremely early KOs. It makes grabbing near the edges of the screen an extremely powerful strategy that makes the other skills you've earned take a back seat. The player camping can just sit there, and unless you've got a good projectile, then you have to approach him if you want the game to continue. So... BANNED, right? Well, no.
The above assumes that the stage in question has
permanent walkoffs. In the case of Delfino, you're "touring" different layouts at a brisk rate; approximately every 30 seconds if memory serves. If somebody is trying to abuse the walkoffs, then they're unable to camp out the other player, since the constant transformations prevent any infinite stalling. The same goes for the walls; you must act within a specific time frame to be able to actually abuse them in a degenerative way, and even then, the other player can simply wait for the next transformation if they're afraid to approach. As such, their abusability is severely hindered, and we have a counterpick-worthy stage.
in the spirit of high-level play, isn't it enough to exercise the honor system on "no stalling/hiding/infinites"?
High-level play doesn't know the term "honor". Competitive players play to win, not to be honorable. If you truly want to win, then you can't box yourself in or hold back, unless there's specific rulings that you can NOT do X action.