Besides that, there is:
The complete ignoring of the origins of a StormTrooper. AKA wtf is with Finn "I developed a conscience" 24702 or whatever.
Since when does this happen? Is he the first? Why is he the first? What The Fuck with no explanation?
Foolish of me to think they would resolve that little issue in Last Jedi ... nope.
Same with Rey "I woke up like this" .i.e. with a lightsaber & suddenly kicks Kylo Ren (a jedi-trainee turned potential Sith)'s ass in a forest?
Explanation in Last Jedi? None - except "Your parents were junkies". LOL great. So there must be millions of level 9 jedis running around the Galaxy who could kick Kylo's ass then?
Your complaints are explained in other media in detail... but there's a lot in the movie's themselves that explain things.
Finn:
The clones were no longer being created, so "the origins of the Stormtroopers", as you said... are no longer in the mix. (though there were several stories of clones defecting or undermining their duty as well) The new recruitment process is obviously people from around the galaxy & not just clones... & so they were not brain washed like the clones were... & so people not digging it are a lot more with the current system. He was not anywhere close to the first. They had an academy where they trained people & they pretty much tried to get everyone on the same page. Many dropped out of the academy... & this was Finns's first job
One story about Finn (from a canon novel) is that he was elite in his training, but his friend was not. During exercises & "situation drills" & stuff in training... Finn tried to help out his friend to get through it, but his supervisor chastised him saying that the weak should be allowed to fall without assistance. Finn didn't like that at all. then on one of his first missions (the start of TFA) he & his crew were asked to mass murder innocent women & children & so there was the obvious disconnect. You really don't even need the other media stuff to understand it... that alone should be enough.
Rey:
Her elite staff fighter skills were well known on Jakku. The scoundrels knew better than to f*ck with her. Her life was literally on the line & so she had to become fierce fighter. The force may of just awakened in her in this movie... but like Anakin was the only human who could pod-race when he was a young kid (before the force awakened in him)... I find it easy to believe that she developed Elite fighting skills that were superior to non-force sensitive people.
Changing from the staff to the sword is pretty easy to understand.
You don't even need the novelization to tell you she was an elite staff fighter. Finn is obviously a lifetime trained stormtrooper & she kicked his ass with her staff.
Other things to consider are:
Kylo had a mortal wound & he only survived it by using the force to keep it together. So he had to focus constantly on that as well as everything else that was going on around him.
He just killed his dad... & so he was a little mind f*cked about that as well.
The main thing though... is that Kylo wasn't trying to kill her... he was trying to recruit her. So he was basically just sparring while she was ferociously fighting for her life.
This is a story about a girl who worked very hard for her abilities. She struggled all her life... had to develop elite fighting skills for survival... & schooled herself off of the computer she had available in one of the crashed ships. That's all she had to do for all those years living alone. So she didn't just wake up one day with all this knowledge & skill. She worked very hard to get it... & being a future force sensitive only helped.