Spoiler
In the original trilogy this is not the case. Obiwan stalls for time, and verbally spars with Vader rather than actually battling with him. Yoda does not train Luke in saber combat and even advises him to eschew his Saber in the cave. And it is only in eschewing his saber in the cave like lower levels of the Death Star Throne Room that Luke eventually wins. When Luke fights Vader in Empire, he is relatively ineffective, a novice and out of his depth. He has clearly practiced more in Jedi, but his style is still a high swinging immature and often adolescent approach, but he builds more evasions into his tactics, overall, he tries to avoid getting into long series of blade exchanges with Vader. He only shocks and overcomes Vader when rage and the darkside suddenly fuel him in a bludgeony and clumsy but effective surprise attack.
All the old forms of saber combat die with the final practicioners at the end of Return of the Jedi. Luke is untrained in it and was never that great. Kylo Ren reflects this perfectly in The Force Awakens. His style echoes Luke's from Return of the Jedi, particularly the bludgeoning and clumsy qualities of his movement. His skillset is broken and at best half formed--like Luke's--and he clearly hasn't encountered anyone else wielding a saber since he fled his training. Rey's time with a saber is similar, you see her adapt some of her staff skills to the saber (I'm expecting her to build a darth maul type of weapon in episode 8 or 9) but ultimately she also reminds one of Luke in her style and usage of the saber.
So I think it's great they didn't try to shoe horn in prequel style saber ballet into these films, instead choosing a deliberate evolution from what one would expect to grow out of Luke's incomplete training and lack of of a lifetime of practice.
Additionally, Luke was something of a mechanical genius (like Anakin), he repaired the droids, ran all the farm equipment, was an intuitive natural pilot and without instruction was able to build a perfect lightsaber. Rey seems to share many of these engineer's abilities and intuitions.
But Ren, once again, is broken and half formed, reflecting his training, and probably his feelings of inadequecy. His saber is clearly of his own construction and it does not function normally throughout the film, it's overlarge, a bludgeon, rather than a finesse weapon, and it sparks and spits and seems on the verge of malfunction throughout the film. even the now iconic shape, I suspect, was a malfunction bug that Ren decided to turn into a feature.
So it then makes sense that Ren is not very good at saber combat, having never fought someone before, anymore than Rey is. He's also not that great with the force, similar in skillset to Luke at the End of Empire Strikes Back. Oh the parlor trick of stopping a blaster bolt in midair is absolutely stunning, he does a wicked force push multiple times, his fall back choice, but he struggles with technique and usage equally often as he uses the force effectively. I love that he is inconsistent like Luke was! it's such a different take on a star wars villain. (and sets up well parallel lightside and darkside training sequences for Ren and Rey in episode 8)
And my final note reflects back to my earlier comment about the original trilogy providing material that become successful Payoffs (not rip offs) in this film. My favorite moment in the film is the lightsaber, in the snow, at the end of the film, and how that scene resolves, a moment that has so much resonance because of its connection to the earlier films. Just brilliant, it works so very very well.
I just wish I knew how and by whom a lightsaber was recovered that went tumbling towards a gas giant when Luke fell out the bottom of the Cloud City ventilation system.