Solution:
Give this to Pegasus and Unicorns
[SKILL_LEARN_RATE:HERBALISM:1]
[SKILL_LEARN_RATE:PLANT:1]
They can still do the job, they'll just always suck at it... almost forever. Your fort may croak by the time they get past dabbling.
I am absolutely against it. Keep bonuses / penalties to skill rates in 50% range. As it is, any caste can learn any skill (except bows IIRC), and be reasonably good at it. 1% learn rate makes no sense at all. In the series all castes were helping Applejack with the harvest.
I like to at least have the option to just ignore castes, and let migrants do whatever jobs they are skilled at. I also don't think that heavily nerfing other castes is a good way to buff Earth Ponies.
From what I see in this mod EPs are the backbone of industry (mining, woodcutting, most animal-related jobs, cooking and processing food, brewing, farming, leatherworking, conjuring wood with woodcrafting, making rock mugs for sale), and UPs do jobs that require skill. Pegasai often get stuck on various walls, and are OK as haulers and military. I find pegasai rather underpowered with their all-around 10% learning penalty.
Another thing You can do to boost a caste is to give them some natural skills. Pegasai could get automatic Competent dodge, EPs be at least Adequate at kicking, and so on.
@ Surp:
You mean in the "Fanon is Magic" version? Worked fine for me, tough my civilisation seems to be lacking a few pieces of armour, meat, leather, and other things.
Did you check if you have points to spend on improving skills? I had to get rid of a few seeds worth 250 to free up enough embark points for everything I wanted. And at this price, maybe I should export seeds instead of crafts.