you have misinterpreted not only that scene where he kills snoke, but literally every single scene with a sith in the series. sith are not "badass". by their nature they are pathetic and fearful.
he didn't embrace the dark side, he just decided he didn't care about anything anymore.
the entire point of kylo ren is that he is not cool. he is not badass. he is desperately trying to be, but the evil heroes he looks up to are empty and hollow. they are not people to aspire to, they are just symbols of human weakness. they will never bring him the peace he wants. on some level he understands this, but he only uses it as an excuse to be more shitty.
he tries to instead reach out to rey, and manipulate her into thinking he's the only one who can understand her, because he doesn't know how to deal with the loneliness and emptiness he feels. he's trying to use her, because he's so laser focused on his own feelings he cant see the bigger picture.
as for what makes him dangerous; he is lashing out in all directions. nothing is more dangerous than aimless, unprincipled evil.
if you look more closely you will see what a blatantly obvious metaphor his character is.