I think you're taking it a bit too harsh. The GM mode is an additional feature, not the main one. And you have to judge it from that perspective. It wasn't even advertised as a killer feature like Sword Coast Legends did, just one of the many.
And I don't understand what's wrong with the idea "up to the community to fill in the monster/NPC ranks and provide levels". They give us the great tools, so why not? This is how the mods working. It's already much more than most of the developers did.
Sure, I'm unhappy that a lot of features from the game editor is not available in GM mode, especially normal NPC movement without possessing them, but the campaign's quality alone justify the game's price. I hope that developers will do some major improvements to this mode, but IMO they should do it as a DLC because it's one of the rare cases I feel that game should cost more than I've paid for it.
