Yeah, she may be the Officer of the Deck at the time when she took command, but really there shoulda been a more senior person on the ship (LT CMDR or CMDR). There wasn't the need for ALL the senior officers be on the planet's surface), and when the bulk of the senior guys are down below, there SHOULD Be a senior guy as Officer of the Deck.
It's a decades-old conceit in Trek to have the command crew beaming down on landing parties. It's a bit late to complain about it now. Heck, the animated episode "BEM" had Kirk, Spock, Scotty, and Sulu all beam down to the planet so that Uhura would be the one left in charge on the bridge (though the animators didn't show her sitting in the captain's chair that time). These things happen in Trek.
Anyway, I think what's more interesting about that part of the book is that the bridge crew Trys is commanding consists entirely of female personnel.
In regards to switching roles...I still annoyed that Kim is now security instead of Command track or Enginneering or sciences. When has he ever even MENTIONED a desire to be a security guy.
Chekov had no prior experience or interest in security before he became security chief in TMP. Worf had no evident security experience before being made security chief on Tasha Yar's death; frankly his only qualification was the screenwriters' racial profiling, assuming that as a Klingon he was automatically the fighting guy. And La Forge was being groomed for the command track before the second-season producers decided to swerve him into engineering. (I still say TNG would've been more interesting with Geordi as the security chief and Worf as the chief engineer.)
Not to mention that Sulu went from astrophysicist in the second pilot to helmsman in the series, and Rand went from yeoman in TOS to transporter chief in TMP. You could even make a case for Nurse Chapel becoming a doctor. Nurses aren't just doctors in waiting, but a distinct and parallel medical profession. So it's a lateral career move rather than an upward one.
The bottom line is that, again, this is fiction rather than reality, and characters get moved to new jobs based on what works for the story.