Scars Unseen
Hero
Well that's explicitly false. The 2E book on the inner planes goes into a fair bit of detail about what can be found in the border and deep ethereal, including the creation and discovery of demiplanes within it. The border ethereal is also utilized a lot in how it interacts with the prime material plane, which makes it possibly one of the most usable planes at lower levels.And, in the case of the Ethereal, it literally DOES only exist to be read about!
As for the rest, I'm not going to go line by line, because I'd mostly just be repeating myself. There is tons of adventuring material for the 2E great wheel, and I'd venture to say that measured against any other D&D cosmology, it would come ahead in that respect by an order of magnitude if for no other reason than TSR put out more volume in those days than any other time in the game's history (rivaled only by WotC's player facing splat books in the 3E era). And for anything that doesn't have a published adventure, that's what DMs are for. Frankly, I can come up with an adventure for any setting at all, given even a rough description of the place. 2E's abstract spell research rules alone could justify going to any of the planes, inner or outer, and the fundamentally lethal nature of many of the inner planes just means that part of the adventure would revolve around research and problem solving instead of just combat.
Now, the thing is, none of this makes the great wheel the best cosmology. No such thing exists, and I'm not trying convince you of anything, really. You don't have to like the great wheel, and I don't need your approval for my own preferences. I'm just putting my own counter to what I feel is a somewhat and unnecessarily dismissive stance on something I enjoy.