A bit of an illustration of how disruptive last year was for the Brawn team:
http://www.autosport.com/features/article.php/id/3150 (Mark Hughes, Subs only)
"In the interests of fairness, we simply said that every department had to lose 40 per cent," said Brawn, something regretfully. "It was as crude as that. We had no other mechanism to go through the company and say, two from here, five from there."
A lot of good people were lost in that cull, not necessarily big names, but engineers that were a crucial part of forming a team's backbone, that helped ensure their departments could run with a certain degree of autonomy. The group that was left was not only shellshocked by the cull and the loss of several key working relationships, but had to establish a whole new dynamic.
Into that mix throw in the departure of a senior member of the engineering staff - Jorg Zander, who left early last year - and it's not really so surprising in hindsight that the car was a little unadventurous. Its gearbox, for example, was too short to make really aggressive use of the twin diffuser.