That is a good point.
Attrition, especially naval attrition, should be part of strategic warfare.
I agree that manpower losses should be part of strategic warfare as is strategic air bombardment and sea-lane interdiction.
Thus,losing the carrier fleet should count as "Strategic losses", on par with with the choking of the convoy routes.
The basic Japanese rationale was sound but far,far too ambitious. Victory as Japan vs the US should be possible, but the Japanese player would need many ahistorical victories,especially naval, to induce sufficient war-weariness to the US because the US is basically a giant when compared to Japan.
I believe that a strategic victory at Midway and subsequent occupation of Pearl (both MANDATORY) would have brought the US to a white peace scenario (or effective cessation of hostilities, which would still be useful for Japan, as pearl would be at the operational edge of fleets based on the west coast, and effectively eliminate the threat of the US island hopping to Japan till after its recapture)