What effect would a couple of extra Royal Navy carriers have had?
Short answerThey would be highly useful, provided the Navy also supplied the escorts and infrastructure needed to operate them.
NotesAdditional Royal Navy carriers would have been useful at almost any point in the Second World War. The hull alone, however, does not create usable naval air power. Each extra flight deck needs aircraft, trained crews, escorts, maintenance, fuel, and shore support. Carrier expansion is therefore a fleet-wide and industrial commitment rather than a simple matter of adding two ships.