For the purpose of ATPL issue, most guys log all PF sectors as PICUS.
Which is not according to the letter of the law for logging the time, and is quite a source of amusement outside of Europe.
Commanding a flight has nothing to do with flying the aircraft - you can be the commander without even occupying a control seat. The commander is the pilot designated by the operator to care for the aircraft and passenger's safety by making a variety of safety decisions. Being designated by the Commander as "Pilot Flying" for a sector has nothing to do with ICUS.