Petal-Morphosis is not a great card, but I have certainly seen it used in many games and it's either great or poor, but the card draw makes it more valuable then you give it credit for. However, your suggestion to change it seem fair and I wouldn't be opposed to it.
Your assessment of Transmogrify however, I could not disagree more with. I main Rose and play a LOT of Citron and I can tell you, those guys have PLENTY of tools to stop and compete against aggro, they don't need ALL their powers to be great against it. You say Transmogrify is only useful:
"1) late game and (or rarely early game) 2) when the opponent has something dangerous on the board that is more dangerous than the worst possible Transmogrify result."
Both of those happen every game that goes past turn 5. Literally. If your deck can't survive until turn 5, your deck is the problem, not the single hero power that *could* have helped you.
As a control player I relish in using both Transmogrify and Goatify (when playing Rose) against my enemy. Those two spells are literally the only ways to successfully win a value battle against cards like Octo Zombie, Portal technician, Imp-throwing gargantuar and Barrel Roller Zombie (to only name a few).
I never want them to change this amazing tool for control decks.