The hate on K8s is misplaced in this case. You should redirect it to containers. Other container orchestration mechanisms will encounter similar, if not the same, issues.
Running out of memory vs wasting memory is also an issue on serverless although somewhat less extreme. Part of the issue is no one knows how much memory their code might use, and we don’t have frameworks that adapt to available memory much. Resource constrained computing is hard.
k8s unfortunately is the only way to maintain sanity if you want to maintain a multi-cloud environment. I don't relish the idea of duplicating functionality but maintaining code across aws lambda's and azure functions.
While I acknowledge you probably have solved for your use-case... I can't help but hardcore LOL at your somewhat terse perspective! Dude... K8S just got mature!