>Muh locked box
The locked box classification is not a good one, and here's why.
1 - In the earlier SCPs, Keter absolutely is about how much of a potential threat an anomaly is. The locked box is a recent retcon from a community that has notoriously made some questionable decisions of late.
2 - Apollyon is still apocalyptic-level dangerous and Thaumiel is still "this one could actually save us", showing how much locked box has been tacked on.
3 - When a classification system makes an intuitive sense immediately assumed by most people (safe is safe, keter is dangerous) and you have to say "no actually, it has a completely different meaning, here let me explain", you have written something both overcomplicated and counterproductive.
4 - Old Keter referred to the general threat level, not only because of the damage it could do, but also how hard it was to contain. With locked box, all you're doing is narrow the meaning, not make it more relevant or interesting.
In short, locked box can and should be disregarded. It's an unnecessary retcon that only makes SCP lamer and more confusing.