This is absolutely not an alternative, not even close. AWS is exactly that: Amazon Web Services. Do you need to host your stuff somewhere else one day? Good luck re-inventing everything from scratch.
I am sort of k8s hater myself, because I've seen very simple and straight-forward production pipelines, reasonably well understood by admins, turn into over-complicated shit with buggy deploy pipelines literally 10 times slower that no one really understands. All of this to manage maybe 10 nodes per service. All of that said, I cannot deny that these new solutions are something that previous generation of ansible scripts and AWS primitives were not. Now we can move all of it to pretty much any infrastructure without changing much. And as much as I hate it, I don't really have an answer to "what else, if not kubernetes?" that doesn't feel a little bit dishonest. I seriously would like to hear one.
Comment on your first point— I have done the work you speak of (porting AWS-specific code to other cloud providers). It is absolutely possible and relatively painless if you design for that feature at the outset. Almost all of the lower level AWS services have a counterpart in the other ecosystems.
So if you build the right interface abstractions around those components, it gets you a long way.
if you are running say a monolith in container in Fargate fronted by ALB that talks RDS PG or Aurora there is not much complexity in moving that anywhere
I am sort of k8s hater myself, because I've seen very simple and straight-forward production pipelines, reasonably well understood by admins, turn into over-complicated shit with buggy deploy pipelines literally 10 times slower that no one really understands. All of this to manage maybe 10 nodes per service. All of that said, I cannot deny that these new solutions are something that previous generation of ansible scripts and AWS primitives were not. Now we can move all of it to pretty much any infrastructure without changing much. And as much as I hate it, I don't really have an answer to "what else, if not kubernetes?" that doesn't feel a little bit dishonest. I seriously would like to hear one.