I suggest that this is the crux of the disagreement. The mental model being applied is one of implicit zero-sumness. You write that the inner planes took up space that could have been used by something else, something more fun to adventure in. But, as many have been quick to point out, the total amount of content devoted to the inner planes was much smaller than that devoted the outer planes. Further, as I stated, this didn't constitute a net loss in adventures, because the rest of the planes existed.
Someone beat me to saying this, but I may as well say it myself.
There is more than just "page space" (which is limited) and "adventure space" (which is indeed unlimited no matter what you do, since you can always adventure
somewhere else if one place is bad), since there is also "conceptual space". This is a truly zero-sum realm, since creating too many things that fill the same conceptual space leads to redundancy, contradiction, and a general weakening of concept. The Elemental Chaos and the Inner Planes take up the same conceptual space, and are incompatible with each other. At the same time, one is superior to the other for a number of reasons (that you may or may not agree with, but are clear to me and many other people).
Also, while "adventure space" may indeed be infinite, the relative value of how much adventure you can get out of any given page count does have its own value, and in that case the Inner Planes are a total waste. Even if they have a small page count, that page-count is still vastly in excess of the usefulness of those planes.
As a note, I can use very similar arguments to describe why I don't a great many of the old Outer Planes. For example, most of the Outer Planes occupy the same conceptual space, even given the alignment wheel. Theoretically, the Great Wheel would work at its best with just eight or nine planes (one for each alignment), and could properly work just fine with as few as four (either one each for law, good, chaos, and evil, or one each for LG, LE, CG, and CE). If the Blood War is central to the Great Wheel, and the vast majority of evil outsiders are from either the Nine Hells or the Abyss, then why do the many other evil planes like Gehenna and Pandemonium even exist? If Celestia is the Lawful Good plane, and Mechanus is the Lawful plane, why do we need to have Bytopia sandwiched between them?
We didn't need to sweep away the inner planes, or turn up the volume on their coolness. Some things in the multiverse can just "be", like the Lady of Pain.
Actually, the Lady of Pain is one of those things that can severely alter a cosmology and the core assumptions of the game simply by existing. There is no way that she can just "be". I don't really want to get into the details, but the Lady of Pain is one of those elements of the Great Wheel and Planescape that leads to the "gods are just cosmic squatters" concept, in which the fundamental structure of the cosmos is presented as being more permanent and fundamental than the actual gods, who are often depicted as impotent and temporary with the greater cosmology and are certainly unable to effect real change upon the cosmology. This is one of my harshest criticisms and dislikes for the Great Wheel/Planescape cosmology, so I certainly won't let you say that you can just let it "be".
Nothing exists in a vacuum, so everything that exists has implications. Often, these implications are more important the the thing itself. This is particularly true for settings and cosmologies, in my opinion.