First, what you say about dead mans hand is simply not right and plainly insulting to all other players not as lucky and "skillfull" as you. It shows how much of aloof many veterans have grown already...
As example for difficulty choice, let me put it this way: you can learn the mechanics of the fights by levelling up and if you don't manage them at one point, you revisit. If the unchained is too hard, you can choose to do the normal version. If you get an undefeatable boss (due to class inbalances) at the ship, you can decide to come back later for another boss. This "choices" have nothing to do with onearmed monkeys.
The point was also not about solo dungeons but scaling dungeons. If for example Oasis and Ravine had scaling loot like forgotten city and breach have for example, they would fit that description too. Besides i mentioned ideally a group version as alternative. Such a system would work for any "side" content or revisitable areas not linked to specific quest chains (which do not suit revisiting).
Second, i was not mentioning gear as the only factor. With certain engine features it is just the "pay attention" model, that makes it hard for some (just try a fight like the ardashir arena lvl80 dust boss while people are teleporting, lagging and freezing all around you. They might do everything right on "their" client, but you'll wipe anyway). You can make fights challenging and interesting without putting up high demands on network and hardware. Back in 2009 it was for example possible to play the whole game without particles enabled (thus only by "paying attention" on what happened and the important things like grim grey god waves showed up on low settings still.). Try that now.
Third, i stand to the use of resources statement. I found simply, that the games who heeded that rule (giving players a choice in difficulty) were the ones with the most replay and longevity factor. But it might be, that i am a bit disappointed from dragonspine in this regard in total.
It was also not specifically aimed at the new instance, but as i said "fixed difficulty" encounters. Back to dead mans hand: Sure, it is solo now, but they could easily open it up for groups if they wanted. The same does not go the other way around as easily.
As with the new dungeon, i bet there is a huge difference in what you need to "figure" out the encounter and later (with tactics known) to grind it. Weirdly, when it comes to judging the difficulty people tend to mention only the second status and forget what was needed at first hand.
So let me ask you a genuine question: If i had patience and average gear and experience with both old world and khitai fights (t1/2 and faction blues or dungeon drops) and a group of likegeared and likeminded friends willing to spent the evening exploring that instance (no loot farmer mentality). Would you advice us to do it? Would there be a point we could not proceed (like a dps race as with yun rau or a period our tank has to survive a certain amount of blows) or do you think it is figureable and beatable in a few hours work?
No need for much spoilers, just an accessment from your experience should do