3 attack points = +15% damage to a stack of skeletons without specialization; if you also take into account the defense, then this is equivalent to a stack of skeletons with +20% damage.
If we use pure logic, then when there were no restrictions on necromancy, as far as I remember, Gaaltran and Vidomina were chosen approximately equally. If the latter had an advantage, then the other heroes would not have been needed by anyone.