"Containers have much greater flexibility than OS packaging: use different libc library easily,"
If you have to use a different libc, that's a kernel engineering problem. On a real UNIX, libc is an integral part of the entire system, is not required to come from another party and is carefully engineered as part of a whole. A good libc requires no alternatives. Case in point: BSD or illumos based operating systems.
"Containers are much easier to use than OS packaging:"
They might be, but that does not make them better, nor does it make them a correct solution, especially if one is running on an illumos based operating system which actually has true containers in form of Solaris zones. Docker is a solution to a non-existent problem, a problem which wouldn't be there if one of illumos-based operating systems is used as a substrate (refer to vmadm(1M) and imgadm(1M) manual pages for a detailed explanation on why that is so[1][2]).
"there are tons of Stack Overflow answers,"
That is symptomatic of poor or lacking manual pages in the system, which in turn is symptomatic of poor or non-existent system engineering practices. Either way, it's an indicator of insufficiently documented as well as insufficiently integrated software: any time one mentions "Stack Overflow", one has lost, because "Stack Oveflow" is full of answers which work, but aren't correct on a system engineering or architectural level, and most who use it to solve their problems don't have the wherewithal to judge that, or they wouldn't be there in the first place. It's a very vicious cycle and a serious, systemic problem with long term consequences detrimental to the IT industry.
If you have to use a different libc, that's a kernel engineering problem. On a real UNIX, libc is an integral part of the entire system, is not required to come from another party and is carefully engineered as part of a whole. A good libc requires no alternatives. Case in point: BSD or illumos based operating systems.
"Containers are much easier to use than OS packaging:"
They might be, but that does not make them better, nor does it make them a correct solution, especially if one is running on an illumos based operating system which actually has true containers in form of Solaris zones. Docker is a solution to a non-existent problem, a problem which wouldn't be there if one of illumos-based operating systems is used as a substrate (refer to vmadm(1M) and imgadm(1M) manual pages for a detailed explanation on why that is so[1][2]).
"there are tons of Stack Overflow answers,"
That is symptomatic of poor or lacking manual pages in the system, which in turn is symptomatic of poor or non-existent system engineering practices. Either way, it's an indicator of insufficiently documented as well as insufficiently integrated software: any time one mentions "Stack Overflow", one has lost, because "Stack Oveflow" is full of answers which work, but aren't correct on a system engineering or architectural level, and most who use it to solve their problems don't have the wherewithal to judge that, or they wouldn't be there in the first place. It's a very vicious cycle and a serious, systemic problem with long term consequences detrimental to the IT industry.
[1] https://smartos.org/man/1m/vmadm
[2] https://smartos.org/man/1m/imgadm