Hmmm... if it's a Youtube video with "Theory" in the title, it usually means no-one actually knows - and the youtubers posting them are just after views. FWIW, TLJ director Rian Johnson has suggested that it's not that significant to the story, outside of being important to Rey herself (i.e. it's a big deal to her, but not necessarily to the SW universe..), he may be misleading us, but it's the closest thing to a proper answer there is for now.
Generally speaking, major plot points about major characters aren't revealed in the books or comics, they tend to fill in a lot of gaps with existing/known back stories or introduce new stuff that isn't required for, or even related to, the films.. so you shouldn't feel like you might be missing big things like that.
... unless you class Darth Maul hunting Rathtars, Wookie Bounty Hunters, psychotic protocol droids, new republic politics, and weird alien races we never see in the rest of Star Wars big things.
