The pilot logs Command, and must be so qualified
That doesn't make sense at all. Why would he need ICUS in that case when he is already theoretically in command by your reasoning and also logs the flight as in command. . ICUS means what is says - "under supervision" As a matter of interest under UK regs (or whatever it is called nowadays) the ICUS pilot is required to make all the decisions and if the pilot in command has cause to disagree with any of the decisions, the ICUS pilot is required not to log ICUS for that flight. It has always been that way and seems common sense reasoning.
I may be wrong what with all the recent regulatory changes that have mystified so many of us since Part 61 came into being. But ICUS in Australia is not in command and never was and must be logged in a separate or specific column to the command column.
That said, cheating is common - with ICUS often being logged in the command column and counted as command time. At the same time the real pilot in command name is often left out. Have personally observed log books like this.