Sona -- Yes, she's in a bad place
So, pre-ability rework, Sona was a positioning-based poke/utility support with a decent balance of skills. (I might be remembering with bias, as she was the champ who got me into the support role, but then I'm also the guy who never bought Thresh). At the time, her numbers were high enough to step up as a solo lane if needed, alongside Karma, Annie, Thresh, Zyra, Soraka and Lux (Note that this was only before the rework, don't roast me for thinking its the current state of affairs). Personally, I am disappointed that she has been nerfed to this level after all the other changes that have been made across the the roster.
Sona's update essentially put a greater focus on her now active-but-shorter time and range auras in exchange for reduced numbers across, and reshaped her ult for reduced width and longer range. Over the patches/updates since then, the numbers have since been chipped at to where she is today.
Now, she isn't in a terrible place, but her position is far from ideal. So, lets take a look at the state of her abilites.
Passive: This has been mistakenly been called reliable CC in the past, but the "charge up" nature forces spamming abilities, which never endears you to the ADC, and a unnecessary mana drain. Even then, the CC is locked to the autoattack, making it less reliable and much shorter range than the slows of most other supports and many other solo lane champions.
Q: This ability has been mostly untouched. Its her primary poke and what the more generous-minded call waveclear. It has a generous ap ratio of .5 but low base damage, meaning you want to build ap to avoid tickling enemies to death. The aura also boost the next attack of you and whoever enters the aura. The only painful thing here is the low base damage, which essentially forces the ADC to do all the damage early to mid game, beyond the pitiful pokes as you build support items, which also means that the damage amp aura is also very lackluster.
W: In theory, this sounds like a nice ability; a heal that heals more when the target is more injured and grands a small shield. The reality is that it's closer to slapping a band-aid on a severed limb. Number-wise, the base heal and ratio is tied for lowest between Alistar's mass heal. With the increasing ratio, her heal beats out Alistar's but still remains lower than any other ally-healing ability. The shield is a mitigating factor, being the only other mass shield besides Karma's enhanced shield, but has the lowest base and ratio of all other ally-shielding and self-shielding abilities in addition to being the shield with the shortest duration of all shielding abilities.
E: This ability was actually improved by the rework, giving a boost to all those who entered in addition to extending the duration on Sona. This ability is pretty good as is, which is the problem, unfortunately. This falls to two reasons; first, only one skill point is needed to make the ability useful as the speed boost doesn't increase too much per level (which is good, as it's already at a good level) and the duration does not increase.
R: With the exception of the new shape from the rework, this ability has remained mostly unchanged for a while, though the ap ratio has been dropped to .5 (which makes sense--she's no APC). The bonuses given from its passive are handy, though there is matter of opinion on whether they should be better off moved into her passive.
So, with all that above, we see one overarching weakness, primarily between the poke and heal: a great need of AP for relevance in any part of the game. For a non-support champ, this isn't much of a problem but Sona is a support, meaning that she has to build 2-3 items before she can really influence a lane or game beyond warding and tickling the other team with her pokes. This is further compounded by the fact that her auras drive her to stay very close to her adc, but her poke/AA range is short, putting a easy bullseye on her squishy frame (lowest base health for a support).
That said, I actually like the idea of her being an aura-based support, though that would require some fiddling with numbers.
As it stands, Sona only has her E and R to set her apart from other champions, due to her high relaince on AP and very lackluster heal ("worst heal in League" is accurate but hurts too much to say directly). Even then, her E has too long a cooldown for anything less than dashing and warding or disengaging and reengaging. Her R on the other hand is a powerful tool with a decent CD and damage across all ranks but i have yet to see a team pick a support based purely on ult (with a one-time exception with a Soraka vs. Karthus).
This is where I'll make my suggestions about what could be done and probably where I'll garner the most hate/agreement.
Health: This could stand to see a small boost, especially as with her short ranges.
Passive: Not much to see here, as I would only recommend upping the base damage a bit to improve her low damage potential.
Q: The ratio is nice, but the poke base damage at early levels could use a bit of a boost. Alternatively, to skew her in favor of her auras, boost the damage for next autoattack both at base and ratio and reduce the poke ratio.
W: Not gonna lie, this one just hurts to look at in base form. Thing is, it looks like it wasn't decided whether its a heal or a shield, and that's bad. My personal take is to boost the base amounts of both heal and shield to reduce the AP reliance and buff the bonus healing ratio to a higher level to curb the current trend of topping off health. The most interesting case would be if the heal ratio were also applied to the shield, but that is unlikely unless the shield is made the focus of the ability. There is absolutely no reason that a mass heal (Alistar) should be able to heal more than a two person heal.
E: I'm not entirely sure what to do here to make this less of a one point talent, which may or may not be a good thing. Here, improvements could range from reducing CD at later ranks or reducing the base at early ranks and have it increase more rapidly to the current amount at max rank.
R: Not much I would want to have changed here, apart from maybe moving the passive bonuses for Power Chord to the passive for clarity.
All things said, I still like Sona as a support even though she lacks consistent CC because of her buffs to the ADC and holds a nice balance between her strengths and shortfallings on paper. Like all supports however, she is matchup and highly skill based.
Well, that's about all I have to say on the subject, so thanks for reading and leave your thoughts!