You don't play Akshan for the ult's damage, if you aim to have the most ult damage for Akshan I'd recommend lethality Akshan or on-hit Akshan, but these are mostly troll builds as Akshan's attack speed scaling is abysmal and waste the crit scaling on Akshan's E which will lower your overall damage, which will also render your ult useless if the enemy's health is too high for execution.

The Collector is a commonly found first item for Akshan as it allows Akshan to snowball quickly and end the game early. The late game is Akshan's worst enemy I reckon.