Mate, I think it’s ‘Mary Sue’ not ‘Merry Sue’? - https://en.wikipedia.org/wiki/Mary_Sue
I agree with a lot (not all) of you what you say above - I don’t think Rey is a ‘Mary Sue’ either, much in the way Luke wasn’t (though he possibly fits the description more than Rey does in Ep4).
It seems to me it is a lazy criticism - not understanding the characters in the SW universe, or not thinking through the events in the film itself as a whole (her environment, how she struggles initially to the events occurring around her, the decisions she makes, then how she evolves and adapts through those situations she encounters etc - ultimately ending with her ‘Letting The Force In’, as it were, to not be defeated by Ren in the lightsabre fight at the end of the film).
An example of a similar sort of lazy and not very well thought-through click-bait ‘journalism’ here:-
Which was quite well retorted to in here:-
That’s not to say there aren’t valid criticisms of the film or the characters therein - as there will be for almost any film out there… but the Mary Sue thing just doesn’t seem applicable to Rey in this film.