It's done the way it is because of the time consumed to finish both of them. Praetorium is longer so it gives more exp, Castrum takes less so it gives less. I won't be against the rewards being even, but there's technically nothing to "fix" so I'm not sure they will do it. Shouldn't hurt if it happens, though, and also shouldn't be hard to do either , so at this point it's just the matter of the demand.
Looking as you joined forum in 2019 I'm assuming you started playing not much earlier (can be wrong as somebody who joined forum more than a year after starting playing). Cutscenes were skippable in the past. This game's playerbase's toxic attitude towards new players became exactly the reason why it was changed and now they are unskippable. Thank the gang that was kicking players from dungeon if they wanted to watch cutscenes and kept saying "watch it in the inn" even though new players deserved to watch it right in the dungeon just as we did when the game came out.Another way to fix it all is to let us skip cutscenes.
The only thing that can change it is DevTeam expanding the Trust system to old expansions so new players could run said dungeons in Story Mode with NPCs at the pace they want. It can happen as, if I recall it correct, Yoshida did say they want to include old dungeons in Trust system as well, but I won't hold my hopes high on that happening in any foreseeable future.
Also, to clarify, the MSQ Roulette exists solely for seasoned players to help new players clear these instances so they could proceed with the story, because without it it took too much time for newbies to wait their queue. The reward for it (which was seriously upgraded with cutscenes becoming unskippable) is a compensation for the time you spend there. Same goes for Leveling and Allaince roulette as well, for example (sweet 5 hours queues to the Labyrinth on Tank flashbacks mmmm), and, to an extend, for all the other Roulettes. It's there to keep old content alive. You aren't forced to do them if you don't want to. If you need to farm your weekly tokens, running last patch dungeon two-three times will be faster.