So just taking Linux kernel bugs as a metric doesn't really apply.
That's why I gave the list I did, as those are the only ones which I'm aware of which can bypass all the layers of isolation in a standard Linux container.
If the ground truth "containers don't contain" applies, then it appears you're saying that Linux is innately and architecturally unsuitable for multi-user/process use, which seems like a fairly bold statement given its prevalence...
After all, all a container is, is a Linux process with Linux isolation mechanisms applied to it...
docker has started adding hardening with SELinux+Seccomp because theres a realisation that the linux kernel bugs keep coming, but this is just a bandaid. the other problem with this approach is that in practice a hardened config is too restrictive for real-user use and has real maintenance cost so most will never use them (as argued by others in this thread for why the gvisor approach is superior). AppArmor is very poorly maintained, buggy, and not a practical solution
Should every organization assume that every attacker has access to Linux 0-days that they can use to privesc on a box?
My opinion is that that's not a realistic assessment for every attacker.
Do some attackers have that? I'm sure they do, but not every company should assume that every attacker will be able to do that.
And all this goes back again to the original point. The trope "containers don't contain" is overly simplistic and not appropriate for every companies threat mode.
Fortunately zerodays aren't commonly used.
In terms of quantity, 4 is not an accurate picture. I haven't sat down to analyze CVEs (https://www.cvedetails.com/product/47/Linux-Linux-Kernel.htm...), but say out of 50 practically exploitable kernel memory corruption bugs/year 4-5 new bugs every year are reachable from some common namespace configuration for a container. And this just marks what is publicly disclosed, which is a subset of the vulnerabilities attackers know about.
Bounties arent the only outlet for these, see: VEP.