This. Basically, Illusion provides raw speed, while Metamorph gives you flexibility and a little more resiliency (I would argue it's less resilient than it looks compared to Illusion though, since Metamorph still eats Grip, Pridemage, Grudge, etc.) Also, if there were ever two cards I could see doing a 1-1 split on, it would be these ones, since they essentially do the same thing, but with different strengths and weaknesses.
Side note: For anyone running
Surgical Extractions in the sideboard, how have you been liking them? I feel like
Faerie Macabre still has game these days, alongside
Tormod's Crypt, plus I'm a little nervous about overloading the deck with Phyrexian mana symbols. But if someone out there is loving the hell out of Extractions, I'm definitely willing to listen.