What do you think of https://github.com/awslabs/aws-serverless-express ?

I think using the Lambda proxy with API Gateway is a major feature enhancement and can be extremely useful as a routing layer for SPAs. If your sole purpose is to use it as a router, then you really don’t have a problem with bloated code.

Add to that the ability lock down access to the actual lambda function by using a custom authorizer on the APIGW paths and it becomes very convenient.