User blog comment:Anon3610/Fairy Forms - Their True Purpose/@comment-2056915-20170805065738/@comment-29197449-20170807033234

The problem with 2 Forms per Season is that one form ultimately ends up choking out the other. Bloomix and Mythix are a weird case because both seemed pretty darn weak, even for more specialized Fairy Forms. Even then, Mythix still comes out on time in more instances as Flora was literally able to defeat Icy as the empowered Snow Queen with hers.
 * Harmonix just seems useless in hindsight since it's really a stand-in for Sirenix should a fairy complete the Sirenix Quest.
 * Butterflix is so underutilized and poorly written that Tynix, the secondary transformation, looks like much more of an upgrade despite only working in what are essentially pocket dimensions.

Heck, Season 4 had multiple secondary forms to Believix and they all fulfilled their purposes, didn't take up too much time and opened up more possibilities for Believix like if there are more powers or "Gifts" compatible with Believix. The 2 subtransformations and 3 different sets of wings all had pretty solid in-universe explanations while also being very obvious business moves made to sell more dolls and merch.