docker service performance vs individual container?

I am running a server with docker-swarm. But then, these days i questioned about docker service performance. I don’t even think that having more than 2 instances and scaling up replicas doesn’t help docker-server performance.

for example,
having a individual container in an instance
docker service with 10 replicas.

In my experience, docker container with an individual container showed better performance(which is getting data from mysql and sending back to fronted.. etc).

Am I misunderstanding about docker container/service performance?

Source: StackOverflow