Of course it's silly to compare Ren in TFA to Vader in ANH. That's a preposterous notion on just about every level.
As for Rey ... I still maintain the "laziness" of the critique using the Mary Sue label. It's too easy to simply dismiss a character wholesale by using it. Your posts improve mightily when actually discussing specific critiques of her abilities - all of which I have said would prove to be valid if her unusual strengths are not properly explained. But considering the mystery surrounding her character, considering the challenges she faced on Jakku, and her crisis of confidence and strength on Takodana, there's likely more than simple wish-fulfillment to her character.
Why is it preposterous? It isn't. What's preposterous is a girl with no experience or training suddenly beating someone with years and years of training. Luke had the upper hand physically on Vader, he had been training and he was no match for Vader at all, it's not comparing Ren to Vader, it's comparing the fights.
And the abilties were unexplained. How does being a scavenger also make you an expert pilot, expert blaster shot after only just being given a gun, expert kendo stick user, expert mechanic etc etc? She is a more competent pilot than Solo, a more competent mechanic than we have seen in any of the movies and without ever having handled a saber before or had any training, does a mind trick and defeats Kylo Ren. I mean the same logic should indicate that old woman she looked at is also a kick ass mechanic, sword fighter, gun fighter etc etc.
She was perfect, she did nothing wrong almost the whole movie and characters seem to regress in combat around her. It became really jarring when she beat Kylo Ren, and then she went off to find Luke. She made Kirk's ascent to Enterprise captain look well thought and pathed out.