I came across a Swarm instance that ran a Minio S3 server at a place I worked at 18 months ago. The actual deployment itself worked fine, but there were fundamental issues with it. The biggest one was that the Minio instance saved all the files to disk and we would have been snookered at the disk failed/instance died etc. However, this was due to the original configuration and not down to Swarm itself. This had a 4TB disk attached on a local network and was able to handle the traffic from ~300 users fine.
I did end up moving this to Kubernetes and deleting the Swarm cluster. The primary motivation for this was so we could reduce the things we were using over any particular desire to increase k8s/reduce Swarm.
The biggest issue with Swarm is not that it's no good, but that because the industry has focused on Kubernetes then the main tooling seems to go into Kubernetes.