So, if you're in a studio (either as EIR or a techie or anything), you get assigned to different startups? Wouldn't this defeat the purpose of entrepreneurship, like pursuing whatever idea you have?

If you are working on your first startup, and are in love with the idea so much, that you would not be able to do anything else, then you might be right.

On the other hand, if your priority is to build a (working, sustainable) company, or become a leader / ceo, then a studio environment could provide you with a better basis for your goals - stability, etc etc