Is there a difference, in terms of mental fabrication, between creativity and imagination (which seem to rely on imagining what's not there) and empathy and mentalizing (which understand how someone's mind/mental affinities are)? Are empathy and mentalizing more 'mindful' and produce less mental fabrication?
As your question implies, creativity, imagination, empathy and mentalizing all have their root in our ability to think abstractly (among other things).
However, I’m not sure that the psychological constructs of empathy and mentalizing corresponds directly to buddhist theoretical concepts, but they can surely be interpreted as components of the brahmaviharas virtues. They are wholesome, since they ameliorate aversion/dosa.
I don’t know, but I suspect that one can’t consider brahmaviharas an actual decrease in mental formations (if one could ever count/measure formations at all), as much as a replacement of unwholesome formations into wholesome ones (according to the principle of right effort).
There is a difference between perceiving and directly knowing. MN1 discusses this at length.
MN1:7.1: They perceive creatures as creatures. But then they identify with creatures … Why is that?Because they haven’t completely understood it, I say.
Perceiving an unopened bottle, one imagines a bottle opener and looks for that. Directly knowing an unopened bottle, one creatively uses what is available to open the bottle, even if it just the edge of a table.
Perceiving a hungry, homeless person, one mentalizes them as outside society and ignores them. Directly knowing a hungry, homeless person, one with empathy shares food.
The difference between perceiving and directly knowing is identity view. Perception is skewed by identity view, tangled in craving, aversion and delusion. Direct knowledge is unembellished, without defilements of craving, aversion and delusion.
With mindfulness, one practices relinquishing identity view. One relinquishes the desire in that. One opens up to direct knowledge.
SN35.95:10.1: “In that case, when it comes to things that are to be seen, heard, thought, and known: in the seen will be merely the seen; in the heard will be merely the heard; in the thought will be merely the thought; in the known will be merely the known.