Is Kylo Ren even powerful at all?

Here is a short answer: NO! Read on to find out why.

Kylo Ren and other force-wielders during this time are NOT powerful at all.

"As time goes on, knowledge is forgotten."

Here is why Kylo Ren and other force-users during that time aren't powerful:

Here is a quote that is worth noting: "As time goes on, knowledge is forgotten." This definitely applies here as well. But first, we need to go back a long time before him.

During the Old Republic Era, that is when both Sith and Jedi alike were at their primes, both in force abilities, knowledge, and scriptures to help their paths. As time goes on, when Jedi were near brink of extinction and Sith too (Talking about during Jedi Civil War and other wars long before Order 66) They lost scriptures as both sides tried to erase memories of each others existence. This happens even when no wars were going on. They lose memories, techniques, abilities because history of them were deleted. During the Fall of the Republic, a Jedi Master then would probably have been only as powerful as a mere padawan during the Old Republic. Now coming back to the Original Trilogy, most records of the Jedi are erased, even then people didn't believe they existed when they existed but 20 years earlier. The only Jedi left: Obi-Wan and Yoda, were both very old and were not in their prime. As they were powerful, they couldn't show their full potential to Luke. The way he was taught to fight was not in any means a fast paced demeanor. And because there were few Jedi texts left, he couldn't really reach a Jedi's full potential. When he starts to trains Ben Solo, he can't teach him much either. The way the Sequels portray their combat is much more fast paced then what it really is. (they did it for show because that's how movies work.) So in reality, Obi-Wan or Anakin in their could defeat both Rey and Kylo by themselves easily. And the old Jedi Bastila in prime could defeat Yoda with even more ease.