I put it to you that the Jailer is a completely ineffective villain. I really don't care about him because I don't find him threatening at all. He just seems like a generic, pantomime villain that I had never heard of before he was thrust at us. Who is he? Why should I care? Even now, several weeks into Shadowlands, we have no real backstory for him.
He just seems incompetenent because the first time we see him he's just monologuing generic lines while we escape his apparently inescapable Maw. Lorewise and gameplay wise we make a mockery of this mysterious villain walking in and out of his domain at will. What were Blizzard thinking?
ILLIDAN/KJ ->THE LICH KING -> Deathwing -> Garrosh -> Grommash-Archimonde (meh) -> Argus (meh, I guess) -> N'ZOTH
...The Jailer?