I feel the biggest issue with Akali is that there is too little things she can do, and even less opponent can do. Playing against Akali, means you either need a team to help kill her, you need to stay far away from her, or you win the stat-check battle against her.
Fighting Akali is closer to a stat-check than anything else, and she have several things that makes her very uninteresting to fight against.
A. She gains lifesteal/spellvamp. This means when she is attacking a squishy she becomes deceptively tanky, and you need to massively outdamage her, and tanks can't kill her, as they rely on wittling opponent down, and she just heals off of them.
B. She turns invisible in her cloud, and it is quite binary in a fight. If you have sweeper or pink ward, the skill become borderline useless to Akali and she turns much much more vulnerable as she relies on waiting for cooldowns a bit. On the other hand if there is no way to see her, she becomes extremely hard to deal with. It's a very binary interaction.
C. More or less a team is required to fight her, but if there is a team around, she struggles big time unless extremely fed. When enemy have exhaust, shields, CC, see-invis, she can't do much about it. She have no fall-back pattern. In case there is not a team, she just kills the target, without much of any interaction, unless she is too weak to do that, then she just fails and can't do much.
D. Limited moments of weakness. Her Q have so short cooldown, it's pretty much always up. Her R being down is just temporary, and with all the stacks she can have it's very hard to play around it, and it's easy for Akali to conserve her stacks until a fight. Ahri have the working version of Akalis ultimate, with clear moments of weakness, and forcing usage of Ahri's ultimate is a big thing. With Akali, forcing usage of one stack is not a big deal, and making her use all her stacks is extremely hard.
E. Low interaction with her. Akali have her main damage tools being her Q and R, both are point and click targeting. If you are within range, you will be hit, and with 3 stacks of her R, you can't escape her, doesn't matter if you have dashs and flash, there is no getting away, as she match your movement with her dashs. Only way to get away is to get under a tower, and win the fight there, or have her give up. There is extremely limited amount of outplay possible against her.
What Akali needs is some combos, more tools, utility and weaknesses. She need to be able to fail, or succeed at a tactical level, and less amount of her power in simple point and clicks. I don't think she can be fixed without a rework, of at least Veigar/Zilean size. Shifting power back and fourth doesn't solve her issues.