But it's never just ECS/Fargate is it. It's ECR, S3, ALB, CF etc.
And at that point you've assembled a stack just as complex as doing it all inside a single k8s cluster.
And at that point you've assembled a stack just as complex as doing it all inside a single k8s cluster.
Also, if you're fair... not all those AWS acronyms you're listing would be displaced by the single k8s cluster. (Maybe you weren't arguing to swap out complexity, rather that the complexity floodgates were open already anyway?)
Very common in fact since many k8s clusters are air-gapped except for a single inbound edge node.