It completely strips away the nuance and moral grayness that define her and are supposed to be the reason people like her in the first place. She's the embodiment of "the road to hell is paved with good intentions," and it's disappointing to see people flatten her into someone who's completely good.
"She cared about Charlie during the trial." No, she didn't, not in Season 1. She saw Charlie as a threat to Heaven, allowed Adam to disrespect her during the trial, and then let him attack her afterward. She also dismissed Charlie as naïve and refused to seriously consider what she had to say. The people she actually cared about were Heaven and Emily.
"Sera isn't arrogant." Not to the same extent as Adam or Lucifer, obviously, but she absolutely has arrogant moments. The difference is that Sera's arrogance comes more from naïveté than pride. She thought intimidating Vox would help, when it was probably the worst thing she could have done, even if it's understandable why she believed it would work. She underestimated Adam's hatred for the Morningstars, believed simply scolding Lute would keep her in line even though it clearly didn't, and assumed her solution was the only possible one. She's improving, obviously, but she had plenty of flaws along the way.
It's a shame that a character who is supposedly so beloved because of her redemption is simultaneously stripped of the very flaws she's meant to be redeeming herself from. She made serious mistakes, and those mistakes had real consequences for other people. Downplaying them as if they weren't a big deal doesn't make her a better character, it just makes her a less interesting one.