I don't see CORE stagnating at all. It's a rock-solid storage appliance, has been and will continue to be.
Both can be true.
Core is (mostly) rock solid, at least compared to SCALE. However, in my opinion it is stagnating, while they prioritize new features, developments, and polish for SCALE.
If you peruse the bug tracker, you'll notice a pattern where fixes are applied for SCALE, but not Core. (Usually with the rationale that trying to fix/improve something on Core might cause breakage.)
"Highlighting or selecting text doesn't work in the Shell."
"Fixed for SCALE!"
"What about Core? It still has this issue."
"Nope. Fixed for SCALE. Not going to touch Core."
"Plugins are broken and/or unmaintained on Core."
"Just don't use Plugins anymore. Have you tried Apps on SCALE? They're great!"
"Oh look! Work is being done to allow non-root admin accounts."
"Cool, right? Only for SCALE."
"Nice overhaul on the menus and UI. Looks much cleaner and more organized."
"Agreed. Only for SCALE, though!"
A new feature or polish (and even "minor" bugs) shouldn't be neglected for the stalwart product due to fear "it might break something". Otherwise, it will
stagnate.
Or how about... get this... a community edition of Core, in which such improvements, polish, and development will not affect nor risk anything on the enterprise product? (E.g, openSUSE to SLES, Fedora to RHEL, etc)
The enterprise customers can keep their version where selecting text in the Shell is broken, while the community users get a product in which you can actually select text as you would expect text selection to work... (The community users will act as "testers" in a sense, so when it's demonstrated that such a fix doesn't cause Armageddon, it can be merged into the enterprise product.)
If this sounds awkward, I agree. That's how I look at the relationship between Core and SCALE going forwards.
(If an alien visited us from another galaxy, and you simply described the development process, they would likely assume "Sounds like SCALE is your professional enterprise product while Core is a secondary product. No way they would have advertised features for the longest time, yet simultaneously admit they're broken and will never be fixed or maintained.")