why is castrum and praetorium not an instance

[Niwashi]

Im just curious if other games go back and do any changes to older content , are is se just following what most games do, Im just of the opinion that all content matters whether its new or old because with new players always joining the game you should want to make the experience work for people from top to bottom

I've never heard of a game company refusing to fix content from the main game when it's as badly broken as this is. (Perhaps it could happen with a minor optional piece of an old expac, but certainly not when it's the final climax of the base game.) And SE themselves does go back and update older content here in this game. Of course that's usually with minor tweaks rather than a significant overhaul like this would turn into, but that's mainly because that's generally all older content needs. Here it isn't.

Sure, you could throw in an NPC party to help, but who would that be? ... It can't be the Grand Company army that's helping you by distracting Castrum's main force, either.

It can't be the main unit of the GC's armies which is busy elsewhere, but a few members who are already assigned to fight under our leadership, that would work. And SE has already said they're planning on allowing our squadron to fight alongside us in dungeons. They haven't revealed yet which dungeons, but I'm hoping these two are the first to be implemented for the feature, as they're certainly the ones that most need it.