She's shown as incredibly gullible, easy to trick, easily starstruck, constantly having crises of confidence and lacking self-worth, getting captured twice, and more or less relying on the support of her newfound friends and parent figure all throughout episodes 7 and 8.
I will agree that 7 and 8 kind of made the First Order into a He-Man villain level threat to the main characters, albeit successfully wiping out the Republic capital and wiping out almost the entirety of the Resistance, but is her not getting her butt kicked yet really that critical of a difference between her and Luke?
And added spoiler tags just in case.
Her 1st kidnapping she escapes with no help, granted she needs help getting off the Star Killer base. She only really has one brief instance where she questions herself and wants to get away from everything and that's resolved in 15 seconds flat. Finn goes through that arc twice. Her 2nd kidnapping which required Kylo's help to escape was her giving herself up trying to redeem Kylo ala Luke trying to save Vader in RotJ
Rey isn't that bad of a character and nothing personally against Daisy Ridley but she could use less obvious plot armor
And that is a fair criticism. But that doesn't make her a Mary Sue, which is more or less meant to imply an almost self-insert everything is easy pretty pretty special princess type of character. ---
Irregardless, for all intensive purposes, I could care less.