Having not worked in the Valley or a startup, I can say the biggest con to me is a lack of stability. You can get a job at BigCo or even MediumSizedButBeenAroundTwoDecadesCo and be reasonably sure you'll still have a job... as long as you want to work there. But with a startup, either they run out of money and you lose your job, they pivot and don't need you and you lose your job, or they get acquired and you very li…
For example (here in the UK) Founders Factory and Forward Partners both maintain large stables of designers, developers and other specialist executors that they assign to their portfolio companies.