Apologies for the late response (was with family and AFK the past week) I will admit I have not looked used functions at all (at Netlify, Vercel, Google Cloud, or otherwise). I've been working in the walled garden of Alphabet internal tools for 9 years and am considering Supabase as a side project.
If successful (and in order to scale the codebase) I'd like to easily support local, dev, staging, canary on prod, and prod environments/functions. I am not sure what the current story is for using or managing functions across those separate environments, but my gut says it would be non-trivial. So my goal would be to have an easy time doing the following:
(1) "start with a single function "binary" that I can deploy, to each environment
(2) add functions to that single binary such that it's easy for me to spin up and debug a local instance.
(3) evolve that binary into a more customized container that has fine-grained controls for scaling instances.
Having written the above, I suppose my main concern around using any cloud function solution is developer ergonomics, which is something I think you're trying to solve for. The supabase-cli is a great start, and it seems to me that adding another container to the mix with my own configuration, image, and functions would be a logical progression.