If you wish to distribute binaries rather than source for users to compile, you can not rely on the system libraries because that can get updated in a non compatible manner any time. Thus you need to package all of them all the way up from libc with your application (basically what windows and macOS apps do). So in regards to the original criticism of elementary not being updated often enough, I do not think it is an issue for development because it gives you a longer living target. As long as you get the security updates.

Usually distros don't change libraries in dangerous ways within a major release. For Debian, "stable" remains as it is for a very long time and even "testing" doesn't change much. Red Hat also maintains the environment stable to a fault. If you want to package for Ubuntu and Fedora, you'll have to probably build for every six-month/one-year release.

We agree. That is why I think that elementary not having the latest greatest libraries (it is an ubuntu lts under the hood) is not a problem and more of a benefit.

Let's say you write an app in Qt, Ubuntu 14.04 (LTS) has Qt version 5.3 but you want to use this cool new feature from Qt 5.7, you can pull the Sources and build Qt 5.7 on your computer and get it working. But obviously when you distribute it, other people who don't have Qt 5.7 installed yet because they are on a LTS distro will not be able to use it.