s
Most influential ult in the game. Can win a team fight with little effort or follow up from your team.
s-
Can single-handedly win a team fight. These ults are guaranteed to get you a pick, keep your team alive, or give yourself another life.
a+
Can win a team fight but with a little bit more effort and help from your team. Also easier to react to and counter than the ults in S tier.
a
Good ults but won't be game changing unless in specific scenarios.
a-
Solid utility ults. These have the potential to win a team fight but won't have huge impact unless you time them correctly and use them effectively. The other team will probably react to them early and reduce their impact in higher elos.
b
Mediocre ults. In the right player's hands, they can be powerful, but are outshined by many other ultimates.
c
Poor ults. Offer very little in terms of value and require the other team to be stupid in order for them to get value. (Zhin ult assuming he doesn't have guillotine).
d
Basically normal abilities. Dredge requires the target to literally stand still for 2 seconds, or have a particularly unaware enemy wander into it for no reason. Io ult will keep you alive for maybe another 2 seconds, and the projectile clips against walls that don't exist, reducing the already measly kill potential. Moji ult requires a second for the animation to run, leaving her exposed, and more often than not requires her to waste one of her two cooldowns to chase down the cookie that is unreasonably hard to catch; if you do manage to eat the cookie, the game locks you in an animation for another 2 seconds where you can't shoot or use any abilities. These are the bottom of the bunch and should be buffed in my opinion.