Yeah I think the mechanic falls flat. I understand the principle, they wanted a way of having independent levelling in the DLC so high level characters could have some build development over its course. But then they put all the content up to end game difficulty anyway, so what was the point?
The only plus side is that they softcapped the blessing level at 12 in a post launch patch, so for everyone short of Radahn, you probably only need to collect 26 fragments. Though this sort of makes Radahn feel even more of a chore, since there's 24 more to get just to eek out a little more damage.
Personally I think they should have just had 10 fragments, and put them behind the 10 Remembrance/major bosses you fight before Radhan (including Bayle). Given the openness of the game, this would have added a nice dynamic about which order to fight the bosses.
Or at the very least they should have made it like Golden Seeds, where there's far more then you need to reach max level. That way you don't need to go to every little out of the way place to hit max level.