Lambda's execution model is language-specific runtimes being fed events off a queue through a single well-defined RPC or RPC-like entry point, with the process

Lambda's execution model is language-specific runtimes being fed events off a queue through a single well-defined RPC or RPC-like entry point, with the process frozen or discarded upon queue exhaustion. So the architecture of Lambda may indeed be a severe mismatch for running arbitrary containers.