No, because renaming it has the same effects on existing systems. The installed package "ownCloud" is no longer there (by that name) so future usage of apt-get can still break.
I'm less familiar with Ubuntu specifically but have extensive Debian experience, so can't comment on the Ubuntu policy, but I suspect Ubuntu views this more as removing a package is them breaking package management on existing systems, vs leaving it as is would still be breaking the system due to the vulnerabilities but not Ubuntu's fault (which I still find arguable, but again it's also just my guess)
Debian stable will also out right refuse to break apt by removing a package, however Debian has a large security patch repo plus a huge backports repo and community - which typically spends their own time back porting patches for newer app versions from the original developers back to older versions the devs stopped patching.
Many years ago at least Ubuntu still did not have the infrastructure for this nor dedicated any man power to the task. Sounds like that is still at least partially the case there.
This is also why ownCloud distributes their stuff in their own repo, which is the best way to go about it (so props to ownCloud there)
That way it is completely up to them how "stable" they want their software to be viewed.
They can either force people to upgrade to a new major version, breaking all existing installs until configs can be updated - or they can try to be stable and backport patches - or anything in between.
It's just mind boggling some dip decided that despite the fact ownCloud has their own maintained packages and even a repo for them, that it would at all be necessary to claim "now i'm the package maintainer!" and put it in Ubuntus repo...
Was this Ubuntus direct doing?
In Debian only the core system is packaged by their own team. 3rd party stuff however anyone can step up and decide to be the package maintainer, compiling from src to debian standards and releasing debs. But it's usually easier to see who to point the finger at in that case.