I don't really agree with the critiques. E.g. GCP will run a Docker container in a serverless fashion, so you can run any language you like using that.
The big issue, from my point of view, is that the programming model takes all the problems of microservices and adds more. Microservices make even trivial features into a distributed system, bringing all the difficulties of reasoning about code that distributed systems entail. Then add an opaque runtime and almost certainly a number of vendor specific services to handle state and other features the serverless model cannot address directly, and you have a recipe for slow development and frustrating debugging.
The big issue, from my point of view, is that the programming model takes all the problems of microservices and adds more. Microservices make even trivial features into a distributed system, bringing all the difficulties of reasoning about code that distributed systems entail. Then add an opaque runtime and almost certainly a number of vendor specific services to handle state and other features the serverless model cannot address directly, and you have a recipe for slow development and frustrating debugging.