Thanks for being forthcoming; and I do appreciate the post. I'm partially venting, and I've been using AWS for a while. Vendor lock-in can be a pain in the rear sometimes.
A lot of the gripe I've got with these posts is that they seem somewhat incomplete. Hard to say things if you've only been messing with it for a week, and don't have a lot of the ins-and-outs of the services. That being said, I've spent at least 2 years diving into lambda and weird issues with it.
I'm not an employee of Amazon, and so my understanding can be off-base as well.
Lambdas are just managed EC2 instances. Each lambda code is stored in an AWS controlled S3 bucket; and on initial execution (cold start) pulled down, and run in their own chroot jail.
I've dealt with java lambdas the most, and I can say that they take your zip, and run the jail inside the zip. They keep your java process open, and just call the handler on each call (warm start.)
Each concurrent call can start another jail on another managed instance; getting the cold start time again.
You can get cold starts by uploading a new zip, or changing any of the lambda compute parameters.
The Golang works in a similar way, jails the zip, and keeps the program running, calling the handler as invokes come in.
I haven't done the python, node, or .NET enough to know if those are the same principles; I'd assume they are.
Interestingly, API Gateway really is just Cloudfront. Cloudfront is just the AWS managed API Gateway.