I'd much rather see Paizo release something that was a little on the weak side, than release a set of overpowered options.
Sure, you can always fix things and houserule them, but for Pathfinder Society play or just dealing with players demands, it's tough when a class starts wrecking your campaign, or telling a player "No" once you've learned your lesson.
If it's weak, then if it's noticeable in game, the DM can make adjustments upward.
Quite simply, players like being given boosts, and hate having things taken away. Since the DM sees the player face to face, it's better to have the "taken away" happen on the designer side.
Houserule the crap out of it? Yeah, I'd houserule it with the ban stick - it's a dreadful class (IMESHO) which does nothing to enhance the game. It fulfills no role that can't be done by an existing archetype, so it's purpose is one-fold: power creep pure and simple. Difference is, I don't really feel the urge to start threads on various boards crying about it.
It was said by a developer (can't remember which) that the APG base classes were supposed to be delving into new mechanics that may or may not be well received. Not being in core makes it easier to disallow if it's not to taste.
Hence the Inquisitor's half-divine caster and round-by-round scaling (which ended up being cut), the mount-specific cavalier with his challenges, the alchemists new casting method, the witch's spell list/familiar dependancy and hexes, and the oracle's divine sorcerer + curses.
In my own personal experience during Beta testing, I had a character playing a heavily modified version of the Summoner.
He was using an Undead version, that was around 100% of the time. I also didn't run it with the magic item sharing thing.
Those two aspects (which have been heavily restricted in the Beta and now final version) never really was an issue. It was the "full healing once per day, but otherwise no healing" that kinda made for an awkward awesome-but-not. And the permanent Large/Huge thing. That made for some pretty easily gained terrifying bonuses that bordered on absurd.
Also, this was a good opportunity to really define a modular creature creation system with evolutions, allowing for more than just the "big brute" idea.
As it was, player's demands meant I had to make some of my own modifications so body type and mode of travel was a little more universally applicable, and rules for Tiny-sized creatures.
In the end, the mechanic is actually quite neat, and I'd love to see a class built around Shapeshifting that used evolutions as it's mechanic.