Maybe the actual text would help, though not really because they're not very specific.
After he becomes a she it seems as if any intelligence is now a foreign thing.
The character seems to lose any sense of self, knowledge, background, personality traits, and life history and literally turns into an 18 year old girl without a lick of basic life sense, let alone the skills a long-time police officer would have acquired. I started to feel as though the author did not like or respect women much and it's more than clear that the author views human personality and skills as determined by gender.
It really would have helped if they'd said what in particular makes her seem like an idiot, because I don't know what they're talking about. Maybe they wanted Stacey to instantly know everything someone who'd grown up as a woman would about for instance walking in high heels or wearing a tampon, though obviously Steve never had occasion to do either.
The last bit in Exhibit B is especially annoying. Stacey doesn't have the skills a long-time police officer would have? Really? (Spoilers!) She coerces an old informant to give her a line on one of the goons who works for the crime boss who unintentionally changed her. That goon she interrogates and then kills in rather nasty fashion. She eludes her former comrades in the police department and uses the dead guy's money and credit cards to set herself up with a lot of nice clothes, as well as a personal armory any NRA member would be proud of. She uses that armory to kill two more goons, walks a couple of miles with a fucking bullet wound, and then undergoes surgery with no anesthetic.
So clearly I'm a huge fucking misogynist who thinks women are delicate flowers and should stay at home barefoot and pregnant. And clearly Stacey has absolutely no police skills at all...WHAT THE FUCK ARE YOU TALKING ABOUT!? DID YOU EVEN READ THE FUCKING BOOK!? Or maybe you were reading the Bizarro world version of the book that's like the complete fucking opposite of what I wrote.
But for the record, Stacey and Steve do operate a little differently. Because hello, their bodies are completely different! Steve was like six-three and over two hundred pounds, so he relied mostly on brute force to get the job done. He was pretty much the bad cop to his partner's good cop when it came to interrogating people; he'd be the one looming over the suspect and threatening to break his face. Whereas Stacey is only like five-six and 110 pounds--and not a lot of it muscle. So obviously she can't loom over people and intimidate them. And obviously she isn't going to be much good in a fistfight against a guy who is the size she used to be. That's not misogynistic; that's just common fucking sense. I mean sure maybe if she had ninja training or something she could fight guys almost a foot taller and twice as heavy, but she hasn't because she just became a girl like a week ago! Duuuuuuuuh.
I don't have a low opinion of all women, but these two "reviewers" definitely are not the brightest bulbs in the bunch.