The reason why I generally dislike working at my big company (wonder if they'll see this!) simply boils down to a lack of challenge
To me this encapsulates the problem we're talking about. The fact that you're coasting and not challenged is exactly the problem. You sound smart and energetic, but the system has still got you down by failing to enable you to find challenges that would benefit the company. Fighting an entrenched bureaucratic culture is a lot harder than you might think (I've spent plenty of time recently doing this!).