Diabolis are very attractive and charismatic beings. Can't see why the other races would neglect interacting with them. People know they can be mischevious, and act around that knowledge. At least that's what my characters do.
With emphasis on
can, agreed. It's the way I RP it as well. However, if interpreting the description less benevolentls (no pun intended), the "can" arguably becomes a "almost always are".
I don't see cats as that impulsive or emotional. Not if you give them some extra wits.
If. However, the starting stats must be representative of the average. This means that only a few do have these exra wits, while most don't. Otherwise, the starting stats would be different.
The races won't likely change. Don't see much of a trouble with that... They're fictional races in a fictional setting. I don't agree with balanced races RPGs.
? Do you want one, or a few, races to be obviously more effective than others? Or do you mean that they shouldn't all be about the same? I agree to the latter, definitely, but not to the first, at all.