Hi,
Plesk is set up in such a way that PHP scripts can't reach other webspaces/subscriptions. Along with the symlink protection, it offers good access separation between websites.
You can also use CGroups to limit resources per subscription.
Using Docker Proxy (can't reach the Docker container any other way) is a big resource user.
I would use a Docker container only for specialised images that require package installation on the Plesk server, like Mattermost, Bitwarden, Elasticsearch, etc.