The same applies to +1 defense for lizards/rakshasa. If you're aiming for a 50% chance to hit, the defense needs to be buffed much more significantly – at least by +3-5 (up to 12-14).
The point of the mod is to make a small number of fundamental changes.
Buffing both demons and pitfiends doesn't align with the goals set for the mod (balancing the tiers).
An aura of nightmares at level 8 or even 9 won't solve anything; the difference is too large to compensate with minor adjustments (if the difference were small, there would be no need to change anything at all).
Regarding nightmares, it's likely that simply increasing the damage of the tier to 10-17 isn't enough. You could swap the damage values, changing the tier from 8-16 to 10-17, and the elite unit from 10-17 to 8-16.