Seems fine to me. 3 to evolve a Bronze, 4 to evolve a Silver, so 5 for a Gold makes sense. As a nowhere-near-end-game player, golds are rare, so sacrificing anything other than a duplicate is unthinkable. Like in the recent tweet about Diamond Evolution, two Gold Bassline Big Bands so easily thrown into the transmutation circle! Climbed out of Bronze just to burn!