These arguments seem to be mostly related to Amazon API Gateway rather than Lambda. (Handling errors on invalid input, returning response codes other than 200.)

These arguments seem to be mostly related to Amazon API Gateway rather than Lambda. (Handling errors on invalid input, returning response codes other than 200.) Lambda was also first available for JavaScript before Python, so probably the JSON event and callback model is a more natural fit for Node.js apps. I would claim that deployment tools like Serverless are relatively safe to use even in production, because once the application is deployed, the tool itself is no longer in the critical execution path. Risks are mostly related to the development process being slowed down if the tool starts failing for some reason. In such situations you can still use Amazon's AWS Console or CLI tools.