Casual player here.
Casual with regard to intent, not time spent in game. When I was happy with the game, I logged in almost every night after work, and at least one full day on the weekends. But, I don't go all out to get through every piece of content as quickly as possible. I took a slow pace with everything, trying to enjoy the game.
Here is where I answer your question about difficulty.
The 'difficulty' was done the wrong way for my tastes.
The difficulty for this game has to do with memorizing patterns and motor memory.
Step One: Get your fight patterns in your motor memory.
Step Two: See the pattern for each fight.
Step Three: Memorize the pattern.
Step Four: Follow your rotation and anticipate the pattern.
In my opinion, that's a crap way to add 'difficulty.' Instead of fights and abilities that reward thinking and strategy, you have one-shot kill and placement mechanics. Instead of being able to creatively use abilities and cross-class skills, being able to creatively use your party makeup to work together, you're all individually following your own rotation. One person misses their placement, or fumbles their rotation, and on the 'hard' content, it's a wipe.
Yes, that makes it difficult but my problem with those kind of mechanics is that it's not challenging. And boredom comes into play, even for casuals, when you realize that once you have the pattern and rotation, it's completely mindless combat. It's artificial difficulty. Since I took things very slowly, it was a few months before I realized exactly what this game is. It's a giant lobby, with progression and gear locked behind instanced, mindless dungeon runs with punishing positioning mechanics.
tl:dr - It's only hard until you memorize the pattern, then it can be ridiculously easy. If you suck at memorizing patterns, have really bad lag, or aren't 100% perfect on your placement and rotations, it's never going to get any easier. (which is why they're adding the echo buff, they know it won't get any easier for certain groups of players)