And yeah if you package stuff against, e.g., the Python libs included in the distro (or EPEL), you essentially need to maintain a repo as a downstream repo of the distro, then rebuild the whole repo with whatever subsequent release as a new upstream when it's time to upgrade. That kind of thing is doable but it's substantial integration work, and if it's aomething you do once a decade nobody is ever going to be fluent in it when it's time to be done.

I think I'd rather just maintain two repos— one against the latest stable release and one against the upstream rolling release (Fedora Rawhide, Debian Unstable, openSUSE Factory or Tumbleweed, etc.)— and upgrade every 6 months or whatever than leap the wider chasms between LTS releases.

And yeah the Python and Python libs shipped in a distro are generally there for the distro's integration purposes, which may involve different goals and constraints than app developers usually have. Building against whatever a distro ships with is not always the best way, as your painful migrations demonstrated.