How does a world replete with powerful magic never use it to improve anyones life? Because most peoples knowledge of that great power begins with the Breaking and ends with the machiavellian Aes Sedai. Imagine a world where everyone was a member of Earth First from birth: If someone offered them refineries that "poisoned the world for the profit of corporate conspiracies" how many would accept? Even the relatively "enlightened" Aes Sedai do not fully nor even MOSTLY understand the One Powers mechanics, regularly being crippled, killed or outright annihilated by the few limited experiments they still attempt. They DO understand and rightly fear their consistently catastrophic history of exploiting the One Power to gain temporal power. So Hogwarts was never on the table for anyone.

How can a world overrun with diabolic and undead beings have NO churches? Because Jordans Creator is a Deist: People DO swear and pray to him, frequently (remember the mantra about the Creator binding the Dark One at the moment of creation, and sheltering the world in the palm of his hand?) The problem is he RESOLUTELY IGNORES THEM in preference to working through inspired intermediaries and champions, lest direct conflict with his Manichean counterpart unmake the world as surely as the Dark Ones victory would. Jordan further rationalizes that by making the whole work a free will parable, despite even a rudimentary grasp of his Abrahamic reference frame showing that supplication and prostration to a deity makes its subsequent intervention wholly consistent with the supplicants free will.

Why does every nation speak with a different accent but in the same language? Please; Tolkien lampshaded that more than adequately with his conceit the ME records were "translated" from the ancient "Red Book of Westmarch," whose "Westron" was actually closer to Old English or Norse than the modern English in which he presented it. If anything, that was LESS excusable because he also "transliterated" the language of Rohan AS Old English.

As for character development, I cannot agree it is nonexistent. Many of the characters do fail to grow any more than superficially, but that lack of growth IS the fatal flaw, not in their characterization, but in their character itself: They are Greek tragic heroes, but that is no more an indictment of Jordan than of Aeschylus. Yet many major characters DO grow, a lot.

Rand begins as a petty farmboy whose largest concern is evading chores, but his reaction to a greater destiny warps him into a defiant and then cold tyrant, then a final epiphany forges a firm but compassionately benevolent leader. At first he has no ambition beyond marrying his favorite village girl, then his goal is bitterly sacrificing himself for an ungrateful world, and at last he is eager both to save the world AND survive doing so before vanishing to avert that worlds permanent dependence on him (one alternate realities Rand witnesses while battling the DO surely includes his existence as God Emperor of Dune. )

Most other main characters grow to varying degrees. Mat is initially more rebellious and lazy than even Rand, but circumstances and friendship gradually evoke his sense of loyalty, which command in turn develops into a sense of responsibility; where Perrin disdains the prestige and luxury of nobility, Mat is fully comfortable with both and merely disdains nobilitys DUTIES, but eventually accepts those as well. Even the negative examples represent change; a "de-velopment" if not development. Perrins honor morphs into neuroses, and Egwenes loss of naivete comes at the cost of her innocence as well; those are not DESIRABLE nor POSITIVE developments, but ARE fundamental alterations adding far greater complexity and depth to the characters.

Many other characters certainly fail to develop, but most are middle-aged (or, in Aes Sedai cases, much older) characters, whose greatest periods of maturity and growth were long behind them before we meet them (although in the case of Aes Sedai, New Spring indicates initiation may slow their emotional aging as much as their chronological aging.)

As for the other complaints, regarding the endings brief and/or casual resolution of elements looming over the whole series—in Armageddons case, the whole POINT of the series—those flaws are serious and undeniable, but less the fault of Jordans declining ability than of his terminal illness. As noted in response to the OP, such clumsy contrived handling is almost inevitable when a fanboy must provide the coda to his own inspiration with his mentors "editor-wife" watching over his shoulder. Between Jordans general outline, Sandersons conscientiousness, Harriets protectiveness and Dohertys loyalty, it may just be a case of too many cooks overcooking the broth.

So I hear what you are saying, but believe some of it overstated and some outright unfair.