Well, first it is a what-do-we-do episode. Second, as a viewer, I really ddn't know what would come next, so that was nice. Would he relapse into a villain (albeit a somewhat sympathetic one)?
It might be said to be "about" the susceptibility to return to old ways/habits; and the power that is found in the purpose of service to others. Seeing Apollo grow even at his advanced age, and seeng Scotty grow out of his hatred were both very nice things. Very Star Trekky imho.
Scotty grew out of his hatred, really? Any conflicts towards Apollo, IMHO, were almost ignored completely, sadly. In fact, I would have enjoyed this episode a LOT more if Scotty had been placed squarely in the center of the action, with Scotty still intensely bitter over Apollo stealing Carolyn's affections, adding his (I presume) failed relationship with Mira Romaine into the mix. Apollo the supremely arrogant Alpha Male bringing out all of these churning emotions to the point of violent conflict...
Now THAT I would have loved to see...AND it would have been a lot more relatable to more people, I would hazzard a guess...