Kassadin Question with Offensive Tree.

Since Havoc (21st point in Offensive tree) only increases your base dmg by 3% and Kassadin has low base damages on his spells, wouldn't the Utility tree be a reasonable choice? 0-9-21 Gives him a safer early game (most kassadins expect to get their ass blasted the first few lvls anyways). I feel like the Sustain in Utility tree, extra gold, mana/mana regen, lower summoner CD/item active CD. Extra HP regen, and the roaming potential for the 21st point in utility could be worth getting over 21 in offense. What am i missing? The late game damage that offensive tree has? Kassadin is going to do a crap load of damage late game with or without 21 in offense.