The systemd slice approach is the same mechanism as containers.
The security problem is being able to talk to the same X server as trusted applications. X clients can do pretty much all the things you don't want Zoom to do; look at your screen, observe your keystrokes, etc. (Sadly, many of Zoom's features, like screen sharing, are also great things for spyware to do in the background. Not saying Zoom does this, but if you don't trust them, this level of access is the part that worries people, not consuming too much CPU.)
The security problem is being able to talk to the same X server as trusted applications. X clients can do pretty much all the things you don't want Zoom to do; look at your screen, observe your keystrokes, etc. (Sadly, many of Zoom's features, like screen sharing, are also great things for spyware to do in the background. Not saying Zoom does this, but if you don't trust them, this level of access is the part that worries people, not consuming too much CPU.)