Board Thread:General Discussion/@comment-15017767-20130809184050/@comment-5927117-20140406164615

Actually 3 temples are needed to able to evolve all. You need  to evolve a dragon 3 times to get it to level10 vs only once in the breeding den. Of course you will sell off most of your dragons at level 1 after a while (why keep double). On the other hand you will evolve some to level 4 just to trade them.

So I guess the reasoning is that after a while it evens out. But I agree that  Evolution time is your most valuable commodity. Never understand it  when I see an Evolution Temple sitting idle.