That is all it goes to. The original plan for Buster Quests was to continue to update it as the only Quest mode for Episode 5, but due to backlash from the players, those plans were changed, so after the second update that added a new "map" and Castle, they were no longer updated outside of some QoL improvements.
Very glad that a very repeatable defense scenario was immediately dropped because they tried to funnel all their "efforts" into it. Looked into what that map was and it seems to be literally the same as Buster Quests, except that you go through a single zone instead of defending to reach the Castrum, talk about peak SEGA laziness.
So we're basically going to get a mediocre Defense mission along with a mediocre map with both sharing the same enemies, and thats gonna be all there is in Episode 5? Does it get any better past this or Episode 6?