If knowing what "should" means helped something, then knowledge of a definition could lead to real actionable information. This seems, on the face of it, absurd.

I think either:

"XYZ things are things that maximize utility"

or:

"XYZ things are things that you should do"

can count as a definition of XYZ, but not both, just as:

"ABC things are red things"

pr

"ABC things are round things"

can count as a definition of ABC things, but not both. (Since if you knew both, then you would learn that red things are round and round things are red.)