Is there any advantage of running k3s if you want to keep etcd? I understand that most k3s performance gains come from etcd being replaced by sqlite but if you still want a HA control plane, sqlite won't cut it.
But in general k3s can be HA without issue and scaled just as well as vanilla k8s. The main advantage of it is that everything comes neatly packed into a single binary whereas the alternative would mean to have a multitude of services running for cluster provisioning.
Kubernetes in the end is basically an API server with multiple componets and k3s puts a nice bow around all of them.