Idk, as level increases, so too should the difficulty. And the difficulty of Dawntrail has been great for normal mode content. It's supposed to be a little harder, that's what makes it fun!
By the time you reach lvl100 and completed the MSQ for all expansions, you probably have put in several hundreds of hours playing the game, and should be well-versed in mechanics and fight design even as a casual player. The devs generously re-use many of the same mechanics across all expansions (spread, stack, gaze, etc.), just re-packaged with different animations. The arena design and boss hitboxes also hint often how big or small an aoe or cleave will be.

Normal raids is optional content too, so if it really is difficult for you, you don't have to do it. You already had all of the MSQ to enjoy, along with all other non-combat optional content to do as well. The difficulty of dungeons in Dawntrail is fantastic and I hope they continue in this direction; I haven't had this much fun in ages :3