The Aribter sending souls to their appropriate places, including the Maw, was literally on the panel. And the Jailer is responsible for keeping those that were selected for the Maw inside there. There was no editorialization of an kind in what @
Al Gorefiend said.
All souls have been going to the Maw lately, so the Arbiter is either dead, helping the Jailer, or being circumvented by some unknown means.
How do you know there would have been any far easier ways to go about it? Was there an abridged Shadowlands mechanics course at Blizzcon that I'm unaware of? For all we know Sylvanas chose the most merciful way (unlikely since she doesn't give a shit about the concept). And even then Blizzard could change their minds 2347 ways before the "big reveal"
If mass Death was required for some non-evil greater purpose, they can accomplish that without causing massive amounts of grief. Personal Sacrifice is a lot less evil than mass murder.
Arbiter is alive from what I got from the panels. And how could have Sylvanas broken intricate mechanics of a realm she didn't even get into prior to her tearing up that portal at ICC?
Sylvanas was clearly able to communicate with the Jailer somehow. Sylvanas has also died a few times, maybe that's when she linked with him in some way, and thus can travel to and from through his power.
How could have the side effect of her anything been the thin destroying the Shadowlands "even if she didn't break the mechanics of Shadowlands"?
Even if she didn't personally break the mechanic, that doesn't mean it wasn't a part of her/Jailer's plan, and the lack of Anima to other zones is killing them. They gain power as more souls go into the Maw, it clearly benefits them so it's incredibly likely it was part of their plan, and if the Arbiter is still alive then they are somehow circumventing it by some means or working with it and it's not something that's happening by accident, that's too convenient.