I don't even think this automatically makes her a Mary Sue. Still, if you're going to do these comparisons, do them with the full context.
Piloting Stuff
Luke
"I used to Bulleye Womrats in my T-16 back home"
Death Star I
We see Luke take out a turret emplacement by over committing on an attack run, but aside from that he does not stand out from his peers. No scoping the Deathstar is him using the force and IS impressive, though he had nothing getting in his way and reached out with the force to nail the shot.
Rey has some piloting experience
Jakku Tie Fighter Chase
Within the space of three minutes Rey goes from being wobbly with an over-sized awkward outdated junker and no co-pilot to assist her (something even Han relies on) to
- Pulling off multiple high powered turns on a dime by stuttering the engines mid flight
- Full on Tokyo Drift
- Doing her own Death Star II interior trench run with no co-pilot or experience flying the ship
- Is able to judge everything perfectly to do the following
Slingshot the Falcon into the air, cut the engines, time out the decent, rotation, and trajectory of the Falcon with the trajectory and speed of the Tie Fighter behind her to then perfectly line up the jammed quad laser with the path of the Tie Fighter so that Finn can hit the fire button and blow it out of the sky. She is able to re-engage the engines, pull out of a spiral, stabilize the ship, and resume a clean flight pattern And then before they hit the uneven terrain and die
I mean, she couldn't of made the shot without Finn to press the button, but she literally no
scoped a tie fighter in an intentional free fall with a weapon that she didn't even have in front of her and couldn't even see.
Rey > Luke
Light saber Stuff
Luke
A NEW HOPE
Luke receives minor training and instruction from Obi Wan.
THE THREE YEAR GAP
Luke spends 3 years self teaching as well as working with the rebels. This includes formal combat training, some light saber training and experience, and at least some interaction with a Jedi Holocron.
THE EMPIRE STRIKES BACK
Luke spent anywhere from 1 to 6 months being training by a Jedi Master <- Link
Pablo Hidalgo: Luke trained on Dagobah for much longer than what ESB shows <- Link
(Also confirms that Degobah has a unique flow of time due to dark side energy [planets that are rich in the force can have this sort of quirk])
Luke gets toyed with, loses his hand, and would have died if not for being rescued.
Rey
The Force Awakens
Rey has no training with the force
Rey has never used a Light saber until she picks it up to fight Kylo
Rey has informal experience (self taught?) with a completely different type of melee weapon
Rey is outmatched by an injured but skilled and experienced Kylo.
She collects herself for a brief moment and then kicks his ass.
Kylo received informal force training in the force from his mother (pretty sure?)
Kylo was trained under Luke SkyWalker for an unknown amount of time
Kylo was further trained under Snoke, but not completely
Kylo has substancial military experience with TFO
Could you have seen Luke winning under similar circumstances? Having literally had no training or held a Light Saber before? I can't.
Rey > Luke
The Last Jedi
Rey
Fought with a light-saber once
Very Minor training from Luke Skywalker (did not appear very light saber oriented)
Seemingly achieved substantial improvement with a Light-Saber after a single fight?
Kylo
No evidence that Kylo had any further training from Snoke
Heck, in TFA she manages to push Kylo out of her head with zero formal training. She over powers him in a display of raw strength and that scene started with her not even having a clue what was going on!
Then she does it
again in TLJ!
I dunno, I think Rey wins the special star child award in this case