First of all - the Namespaces and Cgroups on Linux are not about security. They are about features.
FreeBSD Jails provide both secure isolation from the host and also provide the separated network namespace and resources with rctl(8) when needed.
To have Linux containers separated and secured you need additional layer for that - like SELinux or AppArmor. Only then Docker/Podman/other/... Linux containers are isolated and secure.
Regards.