Definitely surprised by this cut.
Ginny is genuinely one of my favorite characters, and I think she has a lot more personality than people give her credit for. It's not really the fandom's fault that movie Ginny was so bland, but it did color most people's opinion of book Ginny.
As far as Ginny not having flaws, I would say that she does have several flaws. She has a temper, for one thing. She, like Fred and George, can be a little mean. Beyond that, she has several character traits that aren't necessarily flaws, but certainly aren't things that work well with everyone's personality. She's very independent and sometimes reluctant to accept help/limitations.
However, part of the reason she comes off as less flawed is that we're seeing her from Harry's perspective. We see her as Ron's nice little sister who's barely on the periphery of Harry's vision, then as Harry's crush, then as Harry's brand-new girlfriend. They're still in the honeymoon period. If we had seen their relationship continue in DH, I think we would have learned a lot more about Ginny's flaws.
I wish that JKR had further developed Harry's relationship with Ginny and Ginny's character. However, I think JKR was in an awkward place because she didn't really want Harry/Ginny to get together too early, nor did she want the will-they-won't-they to be the focus of the later books. So she tried to develop Ginny's character without drawing Harry's attention to her. The books are sprinkled with references to Harry and Ginny sharing a joke or references to Ginny's changing character, but JKR deliberately kept Ginny sidelined.
JKR wanted to keep the focus on the trio. If Harry/Ginny became involved romantically, either Ginny would become a fourth member and turn the books into an extended double date or people would be annoyed at how often Harry seemed to blow off his girlfriend. The second problem with introducing Ginny as a main character too early is that Ginny makes Harry happy and serves as a de-stressing influence/confidante. JKR needs Harry to be angsty. JKR doesn't want him to be able to talk to someone about his feelings about Cedric, Sirius, his role as the chosen one, etc.
Yes, I wish we had seen more of Ginny. But what we do see in books of her character makes her seem like a good choice for Harry and a lovely person. She is bold, quick, fun, perceptive, understands Harry's needs, and has a lot of integrity.
One of my favorite early Ginny moments is when she accepts Neville's invitation to the Yule Ball, only for Ron to suggest she go to the Yule Ball with Harry. So many 13-year-old girls would have dropped Neville Longbottom like a hot potato if it meant going to the Yule Ball with Harry Potter. But not Ginny.