He was only a Lt JG on the command track by the time he transferred I think. And while he's been a Commander for 20 years, he's been based in the ships' lower decks for that time.
To suddenly become responsible, full-time, for a Galaxy-class ship is too much of a stretch..
1.This is not His first time commanding a galaxy class , in the arsenal of freedom episode, he saved the ships from the attack drones, when most of the senor staff was traped on a planet
2. like they stated he is a 20 yr vet , which means he has exprince commanding people even if he is only in chareg of one dept, after a while it becomes second nature, and gerodi did not just go with the flow he stated many times he felt out of place as Co, but as a 20 yr vet he will not show that in front of his crew
3. Starfleet has suffered many losses mostly in line officers who are very hard to replace, its a surpise that many of picard senior people have not been given their own command hell the only reason wolf might not have been offered his own command is becasue of his reprimands or he might have been offered one yrs ago
It sound to me like you went in thinking of this as a tng book