What I really mean to say is that most startups are using AWS. While you don't have to work at AWS to get AWS skills obviously, having worked there would potentially signal that you really know AWS well and can bring that knowledge into the cooler/smaller company. The interview process is fairly difficult, not google/meta level, but not a walk in the park.

I don’t think that’s the case. When working on AWS, you’ll be assigned to a team doing some AWS product and so you’ll probably get to know it really well, but you’ll be more or less oblivious about the other 50+ products. Whereas, as a mere user of AWS, you’ll get more rounded knowledge.

We've had guys on our team recently get some patents issued in their name, because what we are working on is a hard problem at a massive scale, and we are solving things that have never been solved before.

I will agree that Amazon has some weird stuff around their internal development environment, which I think is well documented elsewhere. OTOH, when you're building services to handle billions of customers all around the world, there are some things you have to do a little differently.