Doran's ring needs buffs.
If it's going to be the only viable start for nearly every mage in the game, it should at the very least be good.
I suggest making basic attacks and single target spells deal 10 extra damage to minions. It ties to the mana gain on kill passive and will help with farming under tower without wasting mana.
all have
in their build and nearly every mage starts at least one of those items. Tweaking their mana and regen will allow them to build sapphire crystal first with either refillable or trip potions to start. They'll lose out on defensive stats early, but make up for it with increased sustain and an item that upgrades into what they're rushing.