While I have no concrete evidence to support this I'm pretty sure the developers scale the difficulty as you progress through the story. Perhaps not for your everyday mobs but dungeon bosses. The thing with Primal fights is that they are meant to be surprising, challenging and new, so there's almost no lead up to their mechanics. Meaning, you either have to learn from dying or have someone guide you/watch a video. As you progress further, you will find that fewer and fewer players have patience to learn by dying so, rather than the difficulty of the dungeon, you begin to worry about the peer pressure.

Since it is easy to over gear new players should have less difficulty with main story instanced content, but mechanics will still stomp you if you ignore them, especially instant-death like getting pushed off the platform in Titan. Oh doing flipping off the platform as a dragoon. You have to see that at least once.

Anyway, dungeons are a team effort. So your tank should be holding hate in a way that reduces damage to the rest of the party, the healer should managing their MP, and others should be trying to avoid damage. (in a simple description) While it does get more difficult it is by no means impossible; ignore the haters and just keep practicing until you get it.