The AI is terrified of unhealth.
Furthermore, they also tend to trade a lot more with each other.
The result is that they tend to have more health resources and this, combined with the fact that the AI puts extreme priority on building health buildings makes the effects of the blight be much weaker on the AI.
Coincidentally, this is quite similar to my own playing style and I have newer been crippled by a blight, ever.
I didn't know that about the AI, and, in fact, I often find they do a poor job of protecting improvements in general and are more inclined to focus on building units rather than health buildings.
Anyway, even if they had the max (and I had plenty too), if Blight affected them the same way, their city of pop 10 would have minimum 50 unhealth. Now, I just don't see them having enough to cover THAT and show no starvation or unhealthy in the city as you can see in the screenshot. That makes it clear that they are not getting hit equally with Blight.
All I am saying is let's either say Blight affects the human player differently, or have it REALLY affect both human and AI players equally. It is not that way now.
The 3 per pop unhealthy you get with Blight might be a bit harsh (especially with the current unhealthiness of the mod), but I can live with that too - you just have to realize you are going down and will stay there awhile before recovering. However, the AI needs to get knocked down too IMO.