Vultr and Digital Ocean are incredibly competitive from a performance per dollar perspective, while still offering a high level of flexibility.

With that said, AWS does offer some features that don't have any equivalent open source solutions (at least that I'm aware of).

The most apparent example of this that is commonly used are Autoscaling Groups, something that is difficult to replicate on Digital Ocean or Vultr unless you intend to write custom code (I believe Openstack or Cloudstack may offer something similar but that's a whole other bag of worms)

Cloudwatch is also an incredibly powerful solution for correlating logs and metrics that can be difficult to replicate without rolling your own solution, which can become quite complex (generally combining something such as Prometheus + ELK + Grafana).

In short, AWS allows you to utilize some incredibly powerful tools without nearly as much management overhead as rolling your own solution.

This is the area where I think AWS excels.