Yes that is what the XO (or Chief Officer on a merchant ship) is supposed to do, but the question is about their ability to do so competently. IF the CO (or Master) is always there and in charge when the ship is entering and leaving ports, or in all difficult situations, how does the XO (Mate) get experience?
I know from the Offshore industry that the Master were/are frequently the only one to actually handle the boat during anchor handling and mooring operations. The Chief Engineer would be the only winch operator.
Some Masters looked at this as “job security”, in other cases it was standing instructions from the company. The result are frequently badly fatigued boat handlers and winch operators.
As sole Rig Mover I would be the same. 36 hr. without sleep would not be unusual, but far from safe.
Then I came on a Norwegian AHTS to witness their handling of anchors in >2000 m. of water off Papua, Indonesia. The Master and Mate did their regular 6 hr. rotation, with the 2nd Mates assisting and operating the winches, also rotating ev. 6 hrs.
Going alongside at the base or the rig was left to the 2nd Mates, but with the Master or Mate on the bridge. A VERY unusual thing for me, who were used to “the way it had always been done”.
You may gain knowledge from schooling and some experience from simulators, but only hands on operation prepares you for the day you are in command.
I know, I have been there and became “instant expert” the day I took command of my first ship, in 1971, (Also in Papua by the way)