Not only that, but there are so many ways to get newer versions of software on Debian Stable when required: backports, Nix, pkgsrc, Docker containers, Appimages, flatpak, snaps...

Debian Stable tends to hand pick the latest LTS version of packages everywhere applicable, so it's actually a good base to standardize on. Packages might be a bit older but they are reliable, predictable, and kept secure by a constant roll of security updates.

In other words, if it doesn't work on the latest Stable, you're probably moving too fast for a good part of the industry. Lots of customer and production stacks are not in the "move fast, release early, release often, and link the crap to the very latest bleeding edge dependency" bandwagon.

If the argument is to enable backports and let it update, what’s your use case for stable vs using testing?

The whole point of stable vs testing is that versions are fixed, reviewed security updates make it, it’s all tested and vetted.

On the other hand, testing and backports haven’t been tested as well and could have issues.

If we use stable and incorporate backports from testing, is it still stable?

If you are selective about the specific packages you are updated, you're closer to stable than you might think.