It's just Magic, there's no Reality Warping in there. Let's say a character had a superpower called "Frost Essence" which followed the idea of making the idea of "Frost" apply to something. By inserting frost into the environment, it could become a frozen environment and thus ice would be created, and it could also freeze attacks midair ("freezing" as an idea rather than its scientific variant) or create a cold that cannot be heated by normal flames or heat because it's not really the lack of thermal energy but the very idea of "frost" inserted in something so that it's now cold.
This would be... the most you'll likely see from Tensei Shitara Slime Datta Ken's magic. It only barely scratches the surface of conceptual manipulation, and most magic is really just "bringing the idea of Fire into reality" like a reverse
All Fictio and therefore creating fire, for example.
When he creates strength, destruction and severance into the sword, he's really just buffing it by making it stronger, more destructive and better at severing stuff. There's no conceptual manipulation, at most properties manipulation or stats amplification.
Now, is it Power Creation? Not exactly, he had that power to begin with, it's just a new application. He's just mastering Magic as it works in the universe, and in this universe magic works by projecting ideas into reality.
How could I explain it... imagine that Mana is a type of energy that, while physical energy pushes physical bodies around, Mana can push an idea into reality, and the more mana you use, the stronger that manifestation will be, so by pushing the platonic form of Fire into reality (not saying it's a platonic form, it could also be just your vision of what fire is), you can create fire. It's also an ideal fire, like an imitation of normal fire, so it might have magical properties due to being a magical thing. This means you shouldn't assume lightning will have lightning speed or or light will be SoL unless outright stated, as even a laser created by magic is the idea of a laser projected materially, not a true one.
