docker swarm also runs on many servers yet i've found its easier to deploy and manage. k8s is super complicated in comparison

How does docker swarm coordinate that an container needs to be started 5 times and how does it balance the load?

you can designate 5 replicas through a service file, its pretty basic but does the job:

services: myservice: image: myimage replicas: 5

you can also determine how many hosts are running replicas based on the current usage and available resources. quite similar to k8s yet easier to manage, at least for me.

i think more of deployment aspects, for docker you literally just install docker and add your hosts, for k8s it's dependent on what you want, rancher, k3s, microk8s or other and setups differ very much on what you might want.