After watching the show for nearly 20 years, I have come to the following conclusion. As much as I like the cast members, there were too many main cast members for this series. Riker and Deanna were the most redundant. Data could have easily been the First Officer and Science officer. The captain should have gone on away missions. On TOS, BOTH Kirk and Spock would travel down to the surface on away missions. When they would get screwed, it was up to Scotty (occasionally Mr. Sulu) to save the ship by being in command. Back in those days, officers were pretty useful and competant. In regards to Deanna, she belonged in an office helping patients, not right next to the Captain. She especially shouldn't be in a position to be Data's commanding officer during a crisis situation. Cobra
Deanna should have spent most of her time, like Dr. Crusher, in sickbay. As a counselor she should, in my opinion, be trained as a medic. Her place on the bridge is to give the captain advice on who they are meeting and to try to anticipate any potential problems. And as she's portrayed in the books (so I've heard) as the Head Diplomatic Officer, ready to meet and great and forge the basis for treaties alongside the captain.
She is not in a position to command Data. In
Gambit, Data takes command of the Enterprise, not Deanna, since he is after Riker in the chain of command. She is outside the command structure, and would only take command in special, rare instances, like in
Disaster. (I do admit Ro should have been in charge, but having Troi in command made some, if convoluted, sense.)
A starfleet captain is a valuable commodity. Finn made it clear in
The High Ground that by holding a starship Captain, especially the one commanding the Federation Flagship, he could call the shots. Having you CO and XO go away on missions would be like putting the President and Vice President in Afghanistan. You could do it, but if something went wrong you're in a world of sh*t. Also, as Troi reminded Riker in BoBW, with Picard kidnapped, he was in Command and needed to be on Enterprise to make the big decisions.
While Data, Geordi and Worf are all capable, competent officers, they should be at their primary post if at all possible. That's why Geordi didn't take over as XO in
Gambit. He was needed in engineering. Worf was given the spot since as XO he could also man the weapons.