RE: Reys fast progression, the ‘Mary Sue’ complaint.
I thought this was explained and dealt with very elegantly in the sequence within Snoke’s chamber. Snoke’s “Darkness rises… and light to meet it” speech clarifies that as Kylo’s dark side power has grown, the Force has found natural balance by also growing the light side. Snoke had mistakenly assumed this growing power was manifested within Skywalker, but in this speech he makes it clear that it was Rey that was the recipient.
I guess the Force forgot to grow the light side when Darth Sidious and his apprentices wiped out the Jedi order and brought tiranny to the galaxy. Every Jedi including Anakin, created by the Force, and Luke have had to work hard at getting control over their Force powers, but Rey just magically gets them, because Kylo Ren stepped on the scene, a poor man’s Darth Vader, and an even poorer Emperor/Supreme Leader. It’s a pretty weak defense in my view.