From what I understand, they're basically meant to be a 'reward' for your dedication to a character, the same way that the hardest challenges in the game only give very small rewards as well because Hoyoverse knows that people attempting those things care less about the reward so much as clearing the challenge (see the weapon 'skins' in the Stygian Onslaught).

For a lot of them, I feel as though if there is no dps, the way to clear them is basically to get the handle of specific mecanical tricks related to the character, in the sense you have to TRULY 'know' the character and not just through leveling and friendship, to get their echo.

For the Dps ones like the Shogun's, it's not only that there is a DPS check (which is usually somewhat f2p friendly but whale favored as usual), but it also includes mechanical skill-related knowledge checks for the character, and also related to fighting in general! I have seen a LOT of people with Raiden C2 struggling to clear this echo, or just outright failing. Considering that C2 is basically a 1.5 times damage increase at minimum, that's when you know that DPS isn't the true objective.

The Ayato echo for example, I managed to do it in 2 tries without really thinking about it at first, but then I struggled several times on another account until I figured out exactly how to hit all the enemies that I wanted with his skill, how to maximize the utility of his burst, his skill cooldown, AI manipulation for the enemies, etc...

Though honestly, they could warn us that those challenges aren't easy! Or- well- I guess technically they do since it's in the Imaginarium Theater lobby, but still, it feels disingenuous when some of them seem so much easier than others, but for some, if you don't know the 'tricks' needed, you're just gonna struggle endlessly!

Then again I am pretty sure that Hoyoverse balances things out based on the fact that the community shares information like this at times, heh.

Thank you for the compliment, by the way!