I concur with @TaranTheWanderer. The banshee's wail is not a sphere area. It simply affects the creatures that meet the criteria for being affected.

I'm not sure I understand what you mean, but I'll give it a shot. I think (maybe) you are saying that the banshee's wail is not an AE (spherical or not). And your second sentence is supposed to explain why. Now, sorry for the upcoming pedantry, but really I am just trying to sort this out in a way that will allow me to reply usefully. Also, it may sound condescending; please just chalk that up to my inability to phrase it more gracefully. I appreciate you engaging in the thread; I'm not trying to insult you.

The way you have phrased that second sentence, it is a tautology, so it's not very helpful in that form. Does this rephrasing reflect your intent?

The description of Wail doesn't define a spherical entity; it just sets out a criterion for selecting the creatures affected.​

Assuming that I've at least gotten close, I think my main point in response is this: whether an effect is an AE is solely a matter of the mechanics; the fiction/fluff does not matter. In particular, for an effect to be an AE, the fiction does not need to include a physical manifestation of the shape of the area. AFAIK, the only things necessary for an effect to be an AE are a) it can affect multiple targets; and b) the criteria for valid targets includes their location; and (probably) c) the set of acceptable locations for targets forms a contiguous region, for some reasonable definition of contiguous that I don't even want to try to think about. Not that anyone would even think about that last bit unless some unholy combination of a rules lawyer and a mathematician got involved.

Anyway, to get back to the point that I am guessing is where our thinking diverges - for many AEs, the fiction does specify a physical manifestation, but that is not necessary. For example:

Fear - You project a phantasmal image of a creature's worst fears. Each creature in a 30-foot cone must succeed on a Wisdom saving throw or drop whatever it is holding and become frightened for the duration.

This is most certainly an AE spell. And "Each creature in a 30-foot cone" is a location-based criterion for the creatures affected in exactly the same way that "All creatures within 30 feet of her" is for Wail. Wail doesn't have to mention the shape of its area because spheres are so easy to describe, but "everything within 30 ft. of a point" is literally the definition of a 30 ft. radius sphere.* Note that you could define the criterion for creatures affected by Fear without mentioning the word 'cone' - it would just be a lot more complicated.

So as far as I can see Wail is certainly an AE, and it happens to be spherical. If you still want to contend that Wail is not an AE, I suggest either showing me why it does not fit my definition, or telling me why my definition is wrong.

Other comments:

As for the dragon breath, I guess I imagine the dragon exhaling very forcefully,so the effect won't spread around corners the way it does for slower-moving effects like fireball and stinking cloud.

I guess it's up for interpretation, but I certainly never got the idea that fireball was at all slow-moving.

It also makes for better game-play by encouraging players to seek total cover from the dragon's breath. But, I'd also buy the argument that the developers simply left off that "extends around corners" text for the sake of brevity and simplicity.

The spirit of Jeremy Crawford appears and intones, "If thing X was supposed to do Y, its description would say so."

This may be one of those areas where the DM's judgement needs to take over; for example, if the dragon breaths fire into a small stone room, the fire might curl around and fill the room even if that's outside of the area of the cone (sort of the way fireball used to fill areas by volume, except without forcing the DM to halt the game and perform multi-dimensional calculus).

I'd only do that if I knew that the players were well aware it worked that way.

Finally, maybe the point of my OP got a little bit buried in my babbling. My intent was to pose the following questions:

Is there a general rule that I have overlooked that answers for non-spell area effects the question(s) that the spell AE rule that I quoted answers for spells?

If not, is it reasonable to conclude that non-spell AEs are supposed to follow the rule (that I quoted) for spell AEs?

And even if we can't decide that it is RAI for the non-spell AEs to follow the spell AE rule, is that a plausible/acceptable/good (your choice) way to adjudicate them?

Any thoughts on those?

* Ok, ok. Technically that is the definition of a closed ball and the sphere is its surface, but that is not a nicety that D&D has ever observed.

ncG1vNJzZmivp6x7prrWqKmlnF6kv6h706GpnpmUqHyvu81mqqmdnKF6or7EmmSenpaasLW%2FjK%2BqZqyfqa6tecKorZ6qXmuCeIKQa2Y%3D