Some AoE Ultimate's currently in the game at level 11:
950 AP + 250% (slow)
Ult CD 100
Charge up skill, normally will never get maxed damage against decent players. Typically resulting in about 475 + 125% AP damage if you're lucky. This also isn't really a quad or penta hit ult like most AoE ults. Since it has a long charge up time typically you're only going to damage a couple players unless you bush cheese and get really lucky. Also gets a shield of 75 + 40% Bonus HP for tanking safely while charging.
250 AP + 80% (root)
Ult CD 130
Probably the closest thing to Neeko's ult in the game. Instant skill, still has much less utility AND AP. Also since it only roots instead of stuns has much easier outplay potential than being hit by a Neeko ult.
AP 40 + 20% (amping up over time) (stun)
Ult CD 120
Kennen's ult hurts, but it can be avoided. Even if you don't avoid it, the stun only lasts 1.25 secs, while his ult lasts 3 secs giving you time to flash out of his radius while he's in Zhonya's. Meaning the most powerful timing of his ult you won't be hit by since his damage increases over time.
AP 125 + 45% (Sec/5 Secs)
Ult CD 110
Fiddle is another DoT ult that can be easy to avoid unless he's single targeting you with CC (which isn't what we're talking about anyways, this is focused around 5v5's). About the only notable thing is that he can ult in zhonya's, otherwise his numbers would be way too weak for how squishy he is. Even then you most likely won't take more than 2 secs of damage from this ult.
425 + 130% AP (stun)
90 CD (Every level)
One of the most powerful things about this ultimate is the fact that the first half of the animation isn't seen by enemies if you're shapeshifted. So you can basically just trigger your ult while shapeshifted and wait for it to be half way over to flash on top of the enemy giving them no reaction time at all.
Basically already looking at the numbers you get an ultimate that can be perceived as an instant cast and does nearly as much damage as a half way charged full AP Nunu. Which instead of maybe getting a couple people if you're really lucky, you could get a quad or penta stun if you're positioned good. You have the lowest cooldown compared to all of these, which is only 54 secs at 40% CDR. This is also the only stun besides the kennen ult, even then kennen ult is much more predictable by the way he travels in lightning form vs the enemy possibly not even knowing you're neeko. On top of all this you get a massive shield on yourself even when all your enemies are stunned (Which honestly this is just a joke at this point). Another thing a lot of people probably haven't thought about is that fact that since this ult isn't a charge ult you can Zhonya's straight as the enemies are coming out of stun just giving another layer of protection.
Honestly I could see comps just running it down with this stupid ult by taking a Ryze ult straight into the enemy, the ult is just that powerful.