So you enjoy people just walking out of your ult? At least with rilaes they get slowed a little.
when you ult in a teamfight, the first thing the enemies will do is try to cc you, not mindlessly run
Youre basically paying 3105 gold for 80 ap.
Not to mention the element of surprise giving you 1+- second of cast time, they wont have time to get away from the range of your ult even without a slow.