I remember when i first got to the titan storymode fight. Random group made via duty finder failed over and over and over again. Every try half the people got knocked over the edge and died. And even when some of us managed to stay on top, we werent doing enough damage to stop the bosses ultimate move and kept dying to it. This went on for like 75 minutes until the group gave up. I was convinced that i would never make it past, and logged off to go to bed. The next night i tried again, as i still needed it for the story. Random group made via duty finder cleared it easily the first try. Halfway through the fight i lagged into a landslide and went over the edge, they still easily beat it without me contributing for half the fight. Moral of the story, the difficulty varies a lot based on the type of people youre teaming up with.

In general, the difficulty of trials and dungeons goes up a little as you go. But its not a ton. If we used a 10 point scale(1 simple - 10 almost impossible) then the low level stuff would be mostly in the 1-2 range, and the hardest story stuff would be 3-4. The hardest content in game is seperated into optional content like the savage raids and the extreme primals. But with the right group the hardest fight is reduced to a 1, and the wrong group can make the easiest stuff an 8 or 9.