Sometimes company trajectories stall out, and you'll end up pressing yourself against the roof trying to push that company back up. Physics will beat you. But! Your founders may get things going again.

As far as your actual questions...

1. There are better work environments, in companies with better prospects.

2. You probably can't change the culture unless you're a founder. But fortunately, your founders can change the culture. The question is whether or not they have the political power to do so in your new ownership context.