The new dungeon is still ENTIRELY too easy

[Valence]

Stone Vigil (Hard) Boss 2
Snowcloak Boss 2 (pre-patch)
Aetherochemical Research Facility Boss 3 (post-patch ironically)
Sohr Khai Boss 3 (pre-patch)
Bardam's Mettle Boss 2
Castrum Abania Boss 2 (pre-patch)
Castrum Abania Boss 3 (pre-patch)
The Burn Boss 3 (pre-patch)

You may notice a lot of these have the caveat of 'pre-patch'. This is because a lot of these bosses had mechanics changed or removed to allow Duty Support. Regardless, these are examples that require some basic problem solving or adequate reactions to clear smoothly.

The kind of difficulty you're bringing up is a completely different type of complexity tied to a completely different type of encounter design and dungeon experience. I am not saying that this is insignificant, but most of what you cite comes from obscure solutions required to clear a boss, solutions not being clearly accessible to the average jane or joe going through said casual content. The difficulty isn't in execution or how to play the content, but in figuring out what the game is expecting out of you, which understandably could make this kind of design bad in other ways.

- Boss 2 of Snowcloak is a perfect example that required people to know they had to aim the snowballs at the boss, although not doing so you'd kill it eventually anyway.
- ARCF is problematic because post patch, this is very much in line with current dungeon difficulty that's all about execution and understanding the DDR patterns. It wasn't as so back then, and the one thing people had to understand was that they had to jump into the tears during the room wide, which is similar to case 1: a boss gimmick. I'm not super fond of gimmicks but that's a different type of difficulty.
- I've never seen people struggling with old Sohr Khai ever personally... And I've ran this countless times in expert roulette with both vets and new players.
- Bardam is literally an old, early version putting out the base lego blocks of the current DDR we're dealing with.
- Castrum Abania boss 2 was definitely a problem, and again, tied to a boss gimmick that was actually lethal to boot.
- Boss 3 is very much an example of current DDR models, but it's true that it had spicy tank attacks that could catch unprepared tanks off, and that's closer to the kind of difficulty the older battle system had. And outlier in casual dungeons though.
- Yeah the Burn killed a lot of parties. A combination of DDR models (the hexa shaped AoEs on the floor) and older battle system mechanics (ice spikes), combined to a boss gimmick (the fog). A pretty hefty concoction.

Still, of the few that aren't tied to bad gimmicks, some are outliers (like mist dragon). Most encounters before ShB were crazy easy. Some actually had great mechanics in the older fashion, but unfortunately could be bruteforced through without even noticing (take say, the second boss of the Aery for example).