That is some complete and utter Bollocks. HMS Victorious had a gallery deck from her Rebuild (Hermes might of, I can’t remember and honestly i can’t be bothered to check this late at night) Eagle was supposed to get one however she only got a half-assed refit (i don’t think it even qualifies as a rebuild) and Ark Royals was even worse than that.
The reason for two islands, (or one long one) is because it allows the funnel uptakes (and thus the machinery spaces) to be spaced out which Improves Survivability. Conventional American super carriers didn’t do this, which reinforces my notion (as a proud Brit) that the Americans are dumb, and Nuclear carriers don’t need funnel uptakes, meaning their islands can be much smaller