Being focused on one thing only also has its advantages. For one, Nomad is very simple architecturally. There's only a single binary for both clients and servers, it also does not need any external services for any coordination or storage.
While other orchestration tools provide much more than just cluster management and scheduling (they also provide things like secrets management, discovery, monitoring, etc.), Nomad follows the Unix philosophy of doing only one thing and doing it well, providing only cluster management and schedulin...
One of the core principles on which ECS is built is the separation of scheduling logic from state management. This way, you can choose to use the ECS schedulers, write your own or even integrate third-party schedulers.
Initially you have to create the EC2 instances that you wish to put in your ECS cluster, using the AMI so that they have the ECS agent on them. However, you have to prescale that specific cluster manually after that.