As the title suggests i have an issue with Sona. Her lack of a core identity, her underwhelming utility, and her just over all lack luster power level in the game.
Lets first address her identity as a character:
Before her rework she was the "super easy aura bot" who could stand way outside a fight and still have huge effects on it. This came from the huge range she had on her auras, the always on nature of those aura's the 1 second persisting effect they had (aura's would say active for 1 second after you switched to a new one), and her super low cooldowns. Her abilities were never over powered in face value (press a button delete/ negate a target), but they offered an insane level of invisible power. This power made it so that she could still be useful to the team even if her ultimate was on cooldown, and provide a lot of power for the laning phase.
After her rework her auras took on a whole different feel. Gone are the always on effect, and invisible power. But so to is gone almost all the range of her aura's. Where you use to be able to skirt the edge of combat ducking in and out, now you need to be front and center to offer your utility skills to your allies. She has be switched from a back line support to a front line support, but was never given the defensive boost to compensate for this switch.
Now to her Utility as a whole:
Her heal first lost the ability to be spammed via increased cooldown. Then lost the ability to be used often with a large increase in base mana cost. After that they reduced the value of each heal with the 50% nerf to her bonus healing. You are now left with a heal that is painfully underwhelming until/unless you build a very large amount of AP, have good mana regen, and have maxed out your cooldown reduction
Lets move to her movement speed skill now. You would think that a skill that can give multiple champions a 10-20% movement speed bonus would be very impressive. However a few issues show up very quickly, the first is that the movement speed bonus only lasts 1.5 seconds on your allies. Sona has the longer base time and a higher movement speed buff but both of these decay down to the aura value, meaning that she cant use them effectively to run anywhere. The second big issue with the skill is that it has a 12 second cooldown. This means that even if you max your CDR you still have long periods of time where you can't cast the spell. Assuming max cooldown, you boost your team for 1.5 seconds and then have 5.7 seconds where the skill can't be used again, that is near 4 times the length of the speed boost.
We can also look at her Q. The bonus damage she offers can not be used on structures so she no longer is good for a siege lane, and won't offer much help in destorying the enemy base. The level of difference between her old 20 AD+AP boost and her new on hit magic damage boost is also questionable. The new skill is much less helpful for champions who do more of their damage in spells instead of auto attacks. There is also reasonable question on if the bonus AD amounted to more bonus damage over all compared to the one time on hit bonus of her current Q.
The killer as i said before is her aura range. You have to be so close to allies to give them any utility bonus that you often have to decide between a combination of safety and personal damage vs helping your teammates.
Finally a few points on her power level over all:
The biggest issue Sona faces is that she is "balanced" around what her skills can do if you tag all your allies. This means that her 1v1 and 2v2 power is much lower then basically any other champion in the game.
However i would like to ask a question, for those who have played Sona. Outside of her ultimate do you ever feel like her skills make a difference? Even if you tag your whole team with a skill, do you ever feel like that made a huge difference? For a champion who is based around helping her whole team, none of her skill ever really feel like they have a big effect if you DO manage to get your whole team with it.
For those who are going to claim she does a lot of damage, ask yourself does she really? Or does she do a lot of damage for a "support"? Would you complain about the level of damage if you were fighting a "mage" character instead? Or would you laugh at how little it does compared to other character of that same classification?