Hunting head hunters

I still can't get what was his point to stay with headhunters in tier 2 when they have their biggest buff in tier 3. No kodo beast with aura, no berserker upgrade, just this spirit walkers as free potions of mana for Blood Mage.
I went in tier 3 rather for getting Paladin, because he lets me easily save the heroes, and he could do the same with Shadow Hunter. He just needed tier 3 tecnoleges and why don't you get it if nobody's stopping you?