CrazyWizard
Shaman
Both the library and the endless scroll have spell fragments as rewards.That makes sense, too of course, so basically it depends on if the libraries hand out a higher proportion of CC or SF... And what you say suggests the latter. Now I really don´t optimize my SF output in my sets, it actually is the only thing I absolutely don´t care about if they get produced or not, but I suppose the libraries alone produce tons as a prerequisite to the CCs.
But since you do not care / doesnt matter you most likely don't even notice it.