Heroku is crap. You can’t deploy without dropping requests, it’s tools are lame and any serious monitoring costs you big $. ‘It just works’ is a layman’s response to the fact that it really doesn’t.
Heroku definitely has a ton more competition these days though. Containerization has really encroached on their main value proposition. Fly.io, AWS ECS and Fargate, Managed Kubernetes, even just Docker on a VPS mostly don't require much more effort than Heroku.
Note that the default was chosen in a world where it wasn't natural that 2 versions of an app could be running side-by-side harmoniously, e.g. due to database evolution.
Yes, it might not work as well when you start to get more traffic, but for getting setup I have no complaints (aside from this downtime!).
The main tradeoff for using EKS is the built-in CNI is limited by the number of virtual IPs you can assign to a given node type's network adapters. If you are running a bunch of small workloads you end up with very under-utilized compute and if you're using autoscaling that results in a lot of churn. We replaced it with weave-cni which has it's own set of headaches in regards to pod access to the control plane but it does allow us to run a basically unlimited number of small workloads on somewhat beefy instances. We set it up using spot pricing and the costs have been very low.