Large companies tend to have enough employees that people tend to specialize - it's an optimal arrangement for them[1]. Your "reward" for becoming the expert with technology "X" is that after a while you mostly get assigned to work with "X".
At a small company, that is less likely to happen. At my last job as an employee in a 2 developer company I would find myself doing high level GUI (WPF/C#), low level computer vision (algorithms/C++) and bit-banging stuff out a communications port while watching the responses from the laser controller using a data logger - all in the same week. A small company can't afford to have a developer dedicated to a single thing so by necessity you wind up wearing a lot of hats and learning a lot in the process.
[1] See theory of comparative advantage https://en.wikipedia.org/wiki/Comparative_advantage
I really dislike the idea of being a specialist. I feel like a dweeb for banging on about disliking "corporate culture". I don't know how else to express that thought.
But yeah, I go crazy if I am specialized / pigeon-holed into only doing one thing all day, every day.
That doesn't prove you're not crazy. ;-) Call it ADHD, but I'd go nuts (nuttier?) doing the same thing every day too. These days I'm doing a computer vision project (C++/OpenCV/3D math) and a laser monitoring project(C#/WPF). I just wrapped up a radar graphics project(C++/OpenGL).
I think finding a job you love and doing that will put more happiness "under the curve" than toiling at a job until you can retire, even if you can retire early.
I love going to work and I've been doing longer than you've been alive - if I was going to burn out it would have happened by now. :-)