Except that isn't the point of a reset ability like that. Akali used to use R as a finisher, because it didn't use energy and the charge got replaced. It means you would R in, start killing, then R to cancel you animations/all that and finish the kill.
Now you see people with 100-150 health survive an ultimate. It breaks the fluidity of Akali's comboing and feels clunky. On top of that when people survive with that much HP you are suddenly forced to do a mechanic that her kit isn't balanced around. You have to either Q or E. If you E and they use mobility you just wasted energy and animations for nothing. As such you generally have to Q them. One of two things happen. They either die from Q, meaning you burned a ton of extra energy since you can't auto attack to proc and regen in, or you aa and that kills them.
Now the purpose of a reset mechanic like Akali R is to go from one kill to the next. If you can't do that then it isn't fulfilling it's role as a reset mechanic. When you burn important energy and cd's just to finish off a target the realistically would have easily been killed by her old ult (Which still didn't do that much damage for an ult) it means you can't go on to other kills.
This further reduces her ability to do what her ult is made to do, get resets and clean up fights. It causes a lot of clunkiness and due to it's lack of damage now lacks synergy with itself and the rest of her kit.
Also for reference all 3 charges only do 150/300/450 (+75% AP) damage.
That is done over the course of 6 seconds. Compare that to lee, which offers a similar amount of utility.
200/400/600 (+200% Bonus AD)
So for a similar amount of utility on an assassin it does less damage and unlike Lee's ult actually lacks synergy with the rest of her kit.
I am not saying it should do a ton of damage, but when it lacks the damage to get resets and clean up fights like it is made to do, and even causes you to have to waste a ton of energy (which in fights is more limiting than mana) then something is wrong.
Even if they just shifted damage from the rest of her kit to it Akali as a whole would feel smoother to play, because right now she is so clunky feeling that I straight up stopped playing her. Not because she is weak, not because she doesn't fit team comps or any other reason like that. Just because her ult feels like the shittiest thing to use. At the point where her autos do more damage than her ultimate either remove the damage and balance around that or shift damage back into it.