Reimu is actually a very flawed character, but that depends on how you see some of her actions. As for me, I like to see them as flaws because that's what makes a character more realistic and in all honestly her flaws are one of the reasons why I like her so much.
For example pic related is from the manga, although Kogasa did a good job, Reimu refuses to pay for her blacksmithing services and decides to test her new needles on her.
Now that was cunt move but hey that's the raymoo I love so is alright. There's a lot of examples like these not returning books from Kosuzu, trying to scam people from the human village, blackmailing Ichirin etc the list goes on , the point is that she can be inconsiderate and mean at times, intentionally or not. But it is what it is and I wouldn't like to change it.
Another fatal flaw is her laziness, which is cute and appealing but in worst cases that same laziness doesn't let her grow or improve, many times she got the opportunity to make the shrine prosper but decided to stop working cause it implied putting effort. Hell she even ate rotten food cause she was too lazy to go grocery shopping, as if she barely takes care of herself.
I dunno what else uh Reimu is also quite mysterious despite being simple minded and brutaly honest, no one really knows what's going on her mind, makes me think that she has to open herself a bit more or something.
I can go on about her flaws but I don't wanna write an essay just to arrive to the conclusion that she's literally perfect in my eyes so I stop here.