The fact that the two bonuses stack separately makes the family-specific damage bonuses inherent to some lines a moot point, since many players already have damage maxed, meaning that any other lines that have things besides family-specific bonuses are actually stronger against said class, e.g.: a player wearing skolver, a BTS, and carrying a CIV will do less damage against undead monsters than an otherwise identical player carrying a leviathan blade.
This does not apply to UV or armor-related bonuses, although OOO should probably consider making armor class-specific bonuses stack separately too.
It should have diminishing effects, else max plus high can lead to a ridiculous damage increase.