I think you're missing the point of the 'serverless' part, as Kong still requires you to have a dedicated server to run it. One of the early stage benefits of the serverless architecture and AWS's api gateway is that you don't have to pay for resources that you don't consume - so if you've only got a small amount of customers, you don't have to pay for dedicated instances to be running.
imho serverless architecture doesn't mean that your app is without servers 100%. Backend still serverless, but everything on top (like an API gateway, load balancer, service discovery, etc) can have dedicated resources.
Fair enough - there are definitely use cases where I could see that making sense. I love the value lambda provides for early stage, when every penny counts.
