It's a word that can be used in place of an argument, because the definition is vague enough to mean whatever you meant it to mean. So instead of having to make specific arguments about why they preferred older games, they can just say "SOUL" and that's that. Then whoever's reading it agrees because they can attach their own definition to it.
Like I'd consider gen 7 to be loaded with SOVL due to all of the small sidequests, lore tidbits about how Pokemon interact with each other in the wild, and the heavy emphasis on fleshing out the culture of the region and how its people interact with Pokemon on a day to day basis. But other people use it interchangeably with "nostalgia".
