If kylo was just a super strong villain with no weaknesses it would've of made things boring. I think his flaws are what makes him compelling. I don't think it's ever mentioned that snoke or kylo are even sith, just that they are dark force users. Kylo himself knows that his weak, which is why i think he is desperate to find Luke so much, to either get luke to teach him how to be stronger or to try to turn luke to the darkside because he knows that he himself will never be strong enough to fill Vaders shoes. He idolises Vader, but also sees Vader's redemption as a weakness and that Vader's work was uncompleted and that he has to finish it. In this age of having powerful and self- confident villains (loki and any marvel villian, khan from star trek, zod from man of steel etc), its kind of refreshing to have such a powerful villian who also has so much doubts about his abilities.
That's an interesting take on it, but I don't really think we're seeing anything new here with Kylo... as I wrote before, he's basically a carbon copy of Anakin - a petulant child who just wants to be powerful but who's potential has yet to be fully realised. For that reason I didn't find him compelling at all, but rather extremely irritating and he was the only part of the film that brought back the bad taste of the prequels.
Snoke was harder to get much of a grasp on, and my gripe with him was more aesthetic; I just don't think it worked in a film that seemed to pride itself on using a lot more practical effects.
As for villains like Khan being too powerful etc, well that's what creates the sense of urgency for the protagonists; they're facing someone who is almost a force of nature and that makes the stakes pretty high. The other thing about Khan is he's an interesting character; his motivations and his anger are actually very easy to identify with - he's been blackmailed by having the people he cares for the most threatened with death if he doesn't do what he's told. When he says in the movie "my crew are my family. Tell me Kirk, is there anything you would not do for your family" (which Cumberbatch delivers with passion that makes it sound pretty compelling) you think "yeah, I get why he's mad. I'd want to f**king kill people if my family's lives were being used to blackmail me".
What is Ren's motivation really? You said it was to "finish what Vader started", but what was that? Vader's motive, we now know, was apparently to save Padme and he just went too far down the bad guy path to go back.
In reality, Ren just seems likea spoiled brat with daddy issues that wants to lord power over others. He's kind of a boring douchebag in my view and there's very little to empathise with.
