The only problem with that is that Docker lambdas boot slower than lambdas with the built in runtime (not ridiculously slow, but could be 2x or something). God help you anyway if you’re trying to do something latency sensitive on Lambda, but if you are then you probably don’t want to add more time for a docker pull.
The situation does keep changing - AWS does optimize things.
I'm not so sure it's a black/white true/false. Depends on what goes in the docker image. It's something like for larger deployments docker is faster but for small deployments it's the other way.
We've actually observed the opposite at our company. Moving from a Python 3.8 built-in to Docker based changed our response times from about 40ms to 30ms on average.
