Why not? The setup I’m experimenting with for an API right now is basically a single Lambda that’s accessible through a function URL (so no ELB/ALB) + an RDS instance. Spinning up additional environments is a single Cloudformation call and deployment artifacts should work with both Docker containers or S3 (depending on the Lambda execution environment).

Seems like a leaner setup than using ECS/Fargate + LBs to me. Have I overlooked something?