• We have updated our Community Code of Conduct. Please read through the new rules for the forum that are an integral part of Paradox Interactive’s User Agreement.
What do we know about rationality, zeal etc? I found a bit on the modifiers page of the wiki but that's very basic information.
AFAIK it's used for some AI weights (perhaps on CBs?), and maybe for some undocumented hardcoded interactions, but overall it doesn't seem to have been widely-used by the devs in the visible text files. If you're writing your own events, you could include weightings for rationality/zeal/etc in the way the AI chooses event options.
 
How many troops did you give them? Did your raid-test AI have the "looters prefer coastal counties" culture/religion feature?

(In my games, viking raiders with 1-2k men seem to manage their raiders fairly effectively - keep their boats close, run away from doomstacks, etc. Similarly, land raiders with 1-2k men seem to understand that they can only get money from adjacent counties. Maybe your issue was that you tried to give sea-raiding troops to an AI who only understands how to land-raid.)

Around 2k raiders for an unreformed germanic. Well, I should playtest it some more, I just did it once to check what happens when spawning troops and then I was really disapointed.
 
AFAIK it's used for some AI weights (perhaps on CBs?), and maybe for some undocumented hardcoded interactions, but overall it doesn't seem to have been widely-used by the devs in the visible text files. If you're writing your own events, you could include weightings for rationality/zeal/etc in the way the AI chooses event options.

I do use it on some checks, I like how it keeps things mysterious unlike if this character has that trait he's going to be a pain or if I'm paranoid these events around rumours of plots are probably fake.

I wondered if things like greed could be one of the key on why some AI farm gold but refuse to build buildings,... I guess the AI will keep some of its mysteries :)