The issue here is you’re comparing the converted value of the 2 books in the new system, rather than their actual value now in the current system. The developers are actually being very generous in the conversion of deed books.
In the current system, 2 books will get you from level 15->16, or halfway from 16->17, and less than halfway at higher levels. The Rainbow Crystal gives more than half enough xp to gain a level at high prestige, so a Rainbow crystal is pretty much worth more than 2 books now. It’s only because the conversion of the books to 16 crystals each is so generous, that they work out better after conversion.
It’s for this reason I think complaining about the imbalance between the level/power->prestige conversion (which is fair IMO) compared with the books->crystals conversion (which is generous) is tantamount to complaining that the book conversion is too generous. Jeto seems to be saying this stuff is set now, so won’t be changed before 9.2, but if changes were still on the cards, I’d worry that complaining about the imbalance would backfire, and get the book conversion nerfed.
I’m satisfied that my maxed kingdoms will convert to prestige 50 (seems very reasonable for level 20 / power 30 to convert to prestige 50). I’m not going to fret that other players who held off on upgrading now get more xp from books than me. I’m just grateful the book conversion is so generous and I’m not going to look a gift horse in the mouth.