I heard rumbling of a beta Dragon Sorcerer in the playtests that gained more and more draconic aspects as they spent sorcery points, but that whole concept was scrapped at the last possible minute to give us the Sorcerer we ended up with. I think they just went with too 'safe' a design for the Sorcerer and as a result the Wizard also suffered from that lack of differentiation. I find the Wizard terribly boring, but it's also that familiar design Wizard fans want, so, really, the Sorcerer is the one that should have been overhauled.
Also, about prep time, "Batman can beat anybody with enough time to prepare".
It was more that
- Dragonic was a poor choice of bloodline to use to preview in a playtest as Dragon Scale and Dragon Strength are very much against the image of the 3e and 4e sorcerers.
- They went too far with the bloodline powers and because of (1), it didn't feel like a sorcerer we knew