I've worked at two startups, then a BigCo, and now another startup. The wearing of many hats was definitely a leveling-up experience, but I felt that I plateaued in just the way you describe. Equity from both of those first two startups is now worth zero.
In my years at BigCo I worked with engineers who have 10-20 years more experience than I do. Often felt like the dumbest guy in the room. I learned a ton. No comparison. But I would never have gotten the job there without my previous startup experience. And without that experience I'm not sure I would even have been able to learn from my BigCo co-workers so successfully.
I got tired of corporate politics and a high traffic commute, so now I'm happily back in startup land.
I feel similarly; I started my career at a BigCo, didn't get much out of it, joined a fairly young company, with (1) more responsibility than someone of my tenure should reasonably have due to (2) high tolerance for failure and (3) they didn't have headcount for the specialized role I was doing. Going back to a BigCo, the experience there was utterly invaluable. I realized that my first go round I had absolutely no idea what I should even be trying to get out of it. This time's different.
There's huge value to getting the lay of the land.
I think there's a similar dynamic with consulting - ThoughtWorks / Pivotal Labs type places. You get shunted around between many different projects, there are never enough people, so there are opportunities to take more responsibilities, and things are often a bit fluid, because a consultancy coming in tends to (should!) crack the organisation a bit. There are downsides to all of that, but it's also a way of getting wider faster, if not getting a lot deeper.
In my years at BigCo I worked with engineers who have 10-20 years more experience than I do. Often felt like the dumbest guy in the room. I learned a ton. No comparison. But I would never have gotten the job there without my previous startup experience. And without that experience I'm not sure I would even have been able to learn from my BigCo co-workers so successfully.
I got tired of corporate politics and a high traffic commute, so now I'm happily back in startup land.