How easily Poe's X-Wing was disabled by blaster rifles but the storm troopers couldn't stop the objectively weaker Tie Fighter when Finn helps Poe escape
First Order TIE fighters are actually shielded, whereas Imperial ones were not. The FO is short on pilots, so they invested in sturdier TIE. It's not clear if Poe's X-Wing is shielded when it was hit. My guess is that shields can't be engaged while landed.
How Kylo Ren was able to just absorb so many blaster/bocaster shots when episode 3 made it seem like Jedis were as vulnerable to blasters as anyone else
Kylo's got the Force running dark side rage to keep him on his feet. You can see him even hitting his wounds to give himself more rage and pain on which to feed.
How an untrained Rey could overpower Ren so easily when a couple days earlier she thought Jedis were a myth
And how the First Order built the starkiller thing without Resistance/New Republic noticing
The rage and pain fueling him made him reckless; as it's been pointed out, Finn's fight with Kylo could have been cut short by Force-throwing him into a tree or choking him or whatever. As it was, he seemed to take little heed of safety or tactics in either battle, and that is part of how he fails to win.
Still other speculation on Rey's skills involve her actually having been a youngling at Luke's academy, but either repressing the memory or having it sealed away from her for her own safety.