Agreed, I think that's the state of the art: if variable concurrency is important, manage your own spare capacity. But I expect AWS and other providers will some day let us pay for reserved capacity without managing it, and I can't wait.
Yeah it seems a like a lot of resources are wasted on useless pings.
It does. But if your endpoint is so inactive that it sits idle most of the time, having it on a server/ec2 instance means you are paying 24/7 for it to sit there not doing anything. You could argue that it's not that much different to pay to keep the lambda warm vs paying for a server to be idle half the time.