Nice suggestion, the only problem with it is that IF they'd release the rates, they could as well remove the event itself, since I can tell you with a clear heart, rates for A, B and all other "rare" letters are shameful and thus they shan't be revealed. One thing I surely know, if something is hidden, it's hidden for a reason, a good reason, to not drive (more) users away from the game...
It was, is and will always be like this, and until whales keep buying tomes from the shop, nothing will ever change, sadly 
PS: Sometimes knowing less makes you happier, njoy being dumb, like me 