Secondary skills in Heroes 3.

For ranged units (including ballistae), Attack doesn't matter, as its equivalent for them is Accuracy... Attack only matters for melee combat.

Yeah, I guess that's exactly what I meant. :D

Interesting Necromancer. Where does he get his leadership from? And why?

Yes, that's a good question... A Necromancer with leadership is like a Druid with Necromancy. :)

Actually, in my opinion, Leadership isn't such a bad skill. I saw negative reviews about it somewhere in this thread... maybe it's not as crucial as, say, mastering a particular school of magic, but it can still be useful.
The more units in a hero-leader's army (well, ideally 7), the higher the chance that someone will attack twice. Sometimes it helps a lot...