Why is Kylo Ren portrayed so inconsistently?

In Star Wars: The Force Awakens, Kylo Ren is the big baddie, the worthy successor of Darth Vader. And even if he himself considers that Vader was much stronger, was he really? We see Kylo Ren displaying some feats we have never seen in the movies – for example, right in the beginning of the movie, he is able to stop and hold the blast of a blaster in midair, even after switching his focus. Then he is also able to read the minds of those he tortures, specifically the mind of Rey, who is in no way a weak-willed character.

But, even so, despite of all his powers, he still gets beaten in the end. He has a hard time in defeating a simple Stormtrooper (Finn), only to be hacked in the end by Rey (who seemingly just discovered her ability to use the Force). Sure enough, he is indeed wounded when fighting in the forest – but when you can hold plasma shot from a blaster in midair, how difficult can it be to overcome enemies as untrained as these two?

Yes, the Stormtroopers are indeed proficient in battle using melee weapons (as demonstrated in the fight between Finn and TR-8R). And yes, Rey is also quite capable in using her staff, as demonstrated when defending herself on Jakku. But they are just amateurs when compared to Kylo Ren.

We guess this is just a simple plot hole, which won’t be answered in the subsequent Star Wars sequels (and, even if they’ll attempt to justify his weakness, it won’t be in a satisfactory way).