SE in L4D2:
1: Tank
2: Witch
3: Smoker
4: Jockey
5: Charger
6: Hunter
7: Boomer
8: Spitter
From those:
2, 3, 4, 5, 6 incapacitate you straight away. That is more than half. Boomer has been nerfed, as well as hitbox for crowning the witch. Still, the ratio of infected-to-incap is...