Well, easy relative to a startup which has just one engineering role (wear all the hats). In the startup world, changing roles generally means going through the interview process at a new company, starting over on seniority, vesting schedules, etc.

I'm sorry to hear about your bad experience at Google. It is a large company, so I don't doubt that there are dusty corners with bad management. But I've seen a pretty broad cross-section of the company and find most of it to be quite great in terms of mobility.