IAM, complicated ? Hardly. You want simple RBAC like the good old times ? You can, just use the "owner" role and move on.

You want any kind of overly thin privileges, for whatever reason ? You can too.

IAM has no complexity per se: the only complexity come from what you want to do.

Saying that "IAM is bad because we can do lots of things" is like blaming a programming language because you can implement whatever you want with it.