The carrier is simply something to help give your fleet a backbone and protects everything in 112 and means you don’t have to land a t bomber in Holland (from Germany). It protects your transports if you are threatening sea lion and can be used to protect sea units at Gibraltar or 127 (Archangel). If you can get it to the Mediterranean Sea it can really help Italy too. The only con is that it does virtually nothing against Russia.
So basically, do you think being in 112 is useful? Do you like to threaten (not take) Sea Lion to help Itake? Do you like hoping Italy in the Med? Do you like taking Gibraltar? Maybe getting South Africa every ten games? Do you like feigning Sea Lion then hitting Leningrad? If you answered yes to any of these, a carrier can be useful.
It does not help directly indeed but indirect.
the ability to project power from SZ127 that you dont have without the carrier.
The ability to shuttle troops from germany to leningrad throughout the game.
Or you could use it to project power in the med, slowing down possible US intervention or help italy and take the middle east.
Yes all not directly against russia the carrier itself does not hurt any russian units but it sure can be vital in making russian life hell.
It should be seen as building an IC somewhere, the IC does not damage units on its own but it will project power in an area.