One thing that may account for this is that the Sims Team does testing.
Certain aspects of the game...are modified for certain players in different "testing groups". While the tuning is the same, something deeper in the game files tells them to behave differently. I believe this pack has 4 testing groups- so there's 4 sets of people out there with 4 different sets of rates and such on this sort of thing.
When they said they will be looking into this in the last laundry list, they meant "We have analytics on how these features are behaving and will be picking the most reasonable looking set and go from there". I wish they were transparent about this.
Even though I am in the high frequency statistic for getting ailments, I also like the chaos (sometimes keeping them for the 3 days, it is too easy getting positive moodlet stacking) to liking the management by having a Naturopath/Apothecary Skilled Sim and Spellcaster Sims to manage the effects (Repairo the broken/burnt things upgrading the low luck quality items, etc.). But it turned my life is easy as a Spellcaster play to high maintenance—a mid range between would probably be best in the long run even for my gameplay style.
