MTGNexus

Who exactly is Hazduhr the Abbot?

Another thing, the Fandom article states that "His knowledge and insight make him an invaluable ruler, but he is rapidly becoming a symbol of the spiritual and societal bankruptcy that is growing within Aysen itself." but it never says how this is happening.

What appears to be meant by that statement is that Hazduhr is a good spiritual leader but by the time of the Homelands story he's getting old and weak, so as he's declining, so is Aysen.

There's not a heck of a lot of more info on him because the Homelands fiction is limited to a comic that mostly covers Serra, Feroz, Sandruu, other PWs, and the Sengirs' various adventures and conflicts rather than the mere mortals of Ulgrotha. There's also some writeups in Duelist magazine around the time of the set's release, and the cards themselves. Beyond that, you'll find slim pickings of characterization or events I'm afraid.

You might find interesting the idea that Innistrad was kind of a modern take on some of the same story themes, with Avacyn as the missing angel goddess instead of Serra and Mikaeus Cecani as the good but ailing and eventually corrupted/zombified spiritual leader instead of Hazduhr.