Mortal1
Superstar
1. A (former) Jedi that's disoriented, immediately after killing his father.
2. Kylo was still able to contain a blast that was killing stormtroopers upon impact (a blast so powerful it was launching their bodies backwards), though the blast of course results in him bleeding out as he faces Rey & Finn.
3. You're making the assumption that Rey had no prior training when she was younger, this may not be the case.
4. Finn also struck him in the shoulder, injuring him further before he duels Rey.
5. Kylo states that "I can show you the ways of the Force", evidently he was not even attempting to kill Rey.
They just setting up Kylo Ren to have that Vader like comeback similar to Empire Strikes Back.
Kylo's got the potential dude already murked his father