"Tolkien's Modern Middle Ages"

[Pitchwife]

Yes, Barad-dûr definitely was a dark satanic mill, more deserving of the title than anything Blake saw in his lifetime. Similar to your description, I imagine the tower itself as the mere pinnacle of a military-industrial iceberg - much of it probably sobterranean, as in Isengard after Saruman changed it (or built into the mountain side). The passage from The Road to Isengard which you quote says that Saruman's New and Improved Isengard was "only a little copy, a child's model or a slave's flattery, of [...] Barad-dûr, the Dark Tower", and I think we can infer a lot, mutatis mutandis, about the latter from the description of the former a little further up in the text:

Originally Posted by LotR Book Three Ch. VIII, The Road to Isengard

Many houses there were, chambers, halls, and passages, cut and tunnelled back into the walls upon their inner side, so that all the open circle was overlooked by countless windows and dark doors. Thousands could dwell there, workers, servants, slaves, and warriors with great store of arms; wolves were fed and stabled in deep dens beneath. The plain, too, was bored and delved. Shafts were driven deep into the ground; their upper ends were covered by low mounds and domes of stone, so that in the moonlight the Ring of Isengard looked like a graveyard of unquiet dead. For the ground trembled. The shafts ran down by many slopes and spiral stairs to caverns far under; there Saruman had treasuries, store-houses, armouries, smithies, and great furnaces. At night plumes of vapour steamed from the vents, lit from beneath with red light, or blue, or venomous green.

I also agree that the idea that Sauron recieving reports or issuing an order by an Orc is absurd. Gorbag describes dealing with a Nazgûl as a harrowing experience; Sauron's own presence would probably have reduced any mere Orc to a gibbering wreck.

As for the sparse population of Middle-earth, I think we ought to remember that we only see the north-west in the book, and that after centuries of war, civil-war and general decline. No doubt Eriador was more densely populated while the North Kingdom flourished. Tharbad, on the fords of the Gwathló, was once a city.

I think the author of the essay you quote is generally right that Tolkien's work in general harks back to an age where towns and cities were fewer and wilderness more widespread, but I'd still maintain that the state of Eriador and Rhovanion at the end of the Third Age, with vast spaces of unpopulated wilderness interspersed with rare pockets of settlements, was untypical.

Rhûn and Harad, where Sauron held sway, are another matter entirely. We know from Tolkien's Notes on motives in the Silmarillion (Myths Transformed section in HoME vol. 10: Morgoth's Ring) that Sauron had no problem with life as such, as long as he could order and control it. We also know that his armies drawn from these countries vastly outnumbered the forces of the West. I therefore assume that his policy in the territories he controlled, rather than aiming at depopulation, would on the contrary have engineered population growth in a precisely planned, supervised fashion, breeding masses of soldiers and slaves according to his requirements. About the means of implementing such a policy I don't care to speculate, but I doubt they involved something as romantic as Mother's Crosses.