In theory though, shouldn't it be possible for the kids to defeat Jack, especially with their guardians helping? Because it seems to me that Jack, while monstrously powerful, can't possibly be stronger than the Troll's version of the Black King, who was prototyped with something like 3 times as many ludicrously powerful creatures, but they still won in the end. I figure Dave's time-spam clones could serve the same purpose Aradia's did, which should help land them the win.
Or at least, Bro shows up with a drill and utterly decimates Jack in their rematch.
This is your big assumption. There are two things that make Jack completely beyond the Troll Black King to the point that he would have been impossible for the Trolls to ever defeat, even with the Aradia army. First, Jack is wearing the queens ring. The Trolls only survived because their plan included having a frogsprite, which kept the black queen of that session from facing them. They only had to face the weaker Black King. Secondly, as powerful as the Glub monster was, he is no comparison to a First Guardian. That monster had the power to kill. The First Guardians have the power to
annihilate.
Even pulling all the Troll shenanigans and a few of their own, there is no comparison to these two foes.
And I'm wondering something. If Jack is Lord English, then Doc. Scratch wouldn't have been so surprised at his appearing, as that is his master. This leads to the ides that each session has their own Lord English, a game construct made to end the session like a cleanup utility. This second idea is supported by Bec jumping into the sprite.