I tackled the Dragon Temple yesterday and got punished for trying to rush in and save Eupha right away (I just wanted a new party member). This is a dungeon where you really need to dedicate at least four days if you explore it as soon as it becomes available. I think devs wanted you to do side quests first, maybe unlock Junah friendship and level up a bit before beating it
I realized this after burning through almost all my MP just to reach Eupha in a chamber at the start of the dungeon. I reloaded my save and went for the "run and rush" approach instead. It's actually possible to complete the dungeon without fighting. When Eupha finally joined, she was at level 41, significantly stronger than my party, but I still beat the bosses effortlessly on my first try using Masked Dancer-Seeker Junah, Wizard MC, and Faker Heismay. Just debuff the boss, buff Eupha as the main damage dealer, and you're good to go—she absolutely demolishes everything. However, she struggles with MP management, so her Summoner Archetype seems better suited for nuking bosses rather than exploring dungeons.
In the end, I gained a new party member, leveled up a a lot from the bosses, and now I'm over-leveled, knocking out side quests dungeons quickly in a day. Once my party hits levels 42-43, I'll return to fully explore the Dragon Temple in one go.