Pedro Martinez's WAR 2000 vs. Gibson 1968: Is the same replacement winning percentage being used?

Pedro Martinez has an 11.7 pitching WAR in the year 2000 while Bob Gibson has 11.2 in 1968. Martinez has a WaaWL% of .834 and Gibson has .754. It looks like that is the winning pct they would each have in the games they pitch if they were added to an otherwise average team. Gibson's lead in IP was 304-217.

If we divide their IP by 9, here is how many games they each had followed by their wins using the above percentages

Martinez 24.11, 20.11
Gibson 33.89, 25.55

Now if we subtract their WAR from these wins, here is how many games the replacement pitcher would win

Martinez 8.41
Gibson 14.35

But Gibson had 33.89 games and Martinez had 24.11. The Martinez replacement has a winning pct of .349 (8.41/24.11). The Gibson replacement has .424 (14.35/33.89). So it seems like Martinez is getting compared to a replacement with a much lower winning percentage. Am I doing something wrong or not understanding WAR correctly? Or is it supposed to work out like this?