Wait...you can only take one job at a time? That's kinda silly.
Yeah, one of the odd flaws about this game. Makes sense for the boss battle area but not for the dungeons. Still is a good game though IMO.
As for the slower text, it didn't really bother me that much, likely because I played Ys Book I and II before starting up GTI for the first time. Ys had REALLY slow text in comparison. Seriously, the ending of part II takes longer than it needs to be because there is a lot of text to have to go through and you can't speed it up. I didn't mind it in GTI that much because at least I loved hearing what everyone had to say and I thought it enriched the experience.
That dungeon made eight year old me very frustrated. Somehow made it to around floor 89 before breaking the music box and fainting to a stupid monster house. The Lava Area where Entei resides is also very infuriating.
So in terms of a super hard dungeon I actually did complete... I think the Kyogre Dungeon in RRT, because in GTI the AI develops incredibly cheap team skills, (But so can I!) and Explorers had no rewards for completing Zero Isle so I didn't bother.