I somewhat disagree with the idea that a Big Corp reduces your learning opportunity. I work for one of the big companies, and one benefit I don't see highlighted frequently is changing specialties. I have worked in 4 different job families over 6 years. If you do work for a Big Corp and you're an effective employee, you can pretty easily work on jobs at the border between the job you have and the job you want. This may be specific to my employer, but I've been able to find ways to demonstrate my (on the job learned) knowledge in a field and get a job I find interesting.
I’d love to explore that more. That is one advantage of bigger companies, more variety of opportunities and if you’re effective you can move between them or define something in between as you point out.
One aspect that I’d like to put words to is something orthogonal to the opportunities, which is the distance of the opportunity from the customer and a ‘real’ problem. This isn’t always true in big companies but at most you’d feel like a cog in the machine no?
