My take:
I worked for a startup as one of their two devs/IT guys at the time (2 business partners who definitely I'd say saw everyone else as employees, three-four customer service types). None of us knew a great deal about dev at the time (no version control, no ticket system, live changes in prod etc..), so we hacked by, but it was only once I worked for a much larger company that I learned a lot of important dev stuff (in my case, I wasn't coming from a CS degree; perhaps more appropriately educated types wouldn't have gained so much). Not all startups are equally tech focused / good at that aspect of things (this one was online retail).
But having said that, the learning payoff tails off really quickly - you gain much more in 3 months on role than the next 3 years etc..
I'd say main thing is to try and switch jobs/roles before you're too comfortable.
Also - focus on what you're gaining right from the start. The thrill of actually having money coming into your account sometimes means you can overlook when you're stagnating. You have to lead your own learning at companies - and if you push for it, you can gain a lot. But generally managers have other things to worry about and if you don't, they'll assume you're happy.
But having said that, the learning payoff tails off really quickly - you gain much more in 3 months on role than the next 3 years etc..
I'd say main thing is to try and switch jobs/roles before you're too comfortable.
Also - focus on what you're gaining right from the start. The thrill of actually having money coming into your account sometimes means you can overlook when you're stagnating. You have to lead your own learning at companies - and if you push for it, you can gain a lot. But generally managers have other things to worry about and if you don't, they'll assume you're happy.