I am sure Rey knows how to defend herself but to best a trained Jedi... albeit a whiny one but still... And his display of control over the force, like stopping a laser bolt in mid air early on only to get repelled by Rey... still a bit far fetch even is she is force sensitive and is most likely a Skywalker.
The lightsaber is not special but the Jedi training is somewhat special. Recall in Episode 4 when Luke was training with the lightsaber? Jedi relies on the force to guide them, to know when and where an attack is coming from by feeling the force (like repelling laser bolts). Surly Ren should be able to control that better than Rey and has more experience. No?
Oh yeah, Finn the janitor held his own, so does the Storm Trooper with the Baton. Which is why I concluded... Luke Skywalker is a lousy teacher and thus he is hiding in shame.
Thank God Ren is not Darth Kylo Ren... Palpatine, Vader, Dooku, Maul and all the Sith Lords before them would be spinning in their graves. 
[Edit]
Or maybe that is Luke's master plan to stop the Sith once and for all. Sith Lords usually seduce and recruit young talented Jedi to become their disciples. If Ren is the best the Jedi has to offer to the Sith Lords, the universe is surly a safer place