Aside from the winrate counter-argument already outlined before, and the healing argument you have which was already refuted, the Sona re-work didn't do anything. Her kit remained the same before and after re-work, but they just took out a bunch of stuff.
Her auras went from an indefinite 1000-range buff to a 3-3.5 second 350-range buff. The auras essentially got gutted to heal.
Her Q's base damage was actually cut, and her aura changed to give a on-off aa buff that gives 20-60 bonus damage on a negligible 25% AP scaling.
Her Q's Power Chord actually went from a 100% damage buff to 40%. Oh, and the cooldown was increased by a second. So a straight nerf.
Her heal's base got nerfed early game, and lose 5% AP (as if 25% AP was something to be proud of at all). At least, the heal is increased by 1% 0.5% for each 1% of missing hp (they nerfed THAT after the rework, also, duly note the heal actually does NOT heal %hp, but increases the flat value by the missing% hp value, so it never actually heals %hp to begin with). Then she grants a 35-115 damage shield with another 20% AP ratio that lasts, what, 3 seconds? As if a shield that small would ever actually last any longer. And the re-work increased the mana cost by 10. And when the heal modifier got nerfed, the increased the mana cost AGAIN by 10. Also, the cooldown is up by 3 seconds. Okay.
Her e was the only thing that got a noticeable early game buff to its base stats, going from 4-12% to 13-17%, with a better scaling to make up for the lost permaura buff. Her allies also get a better, temporary movement speed buff, but now the cooldown is at 12 seconds, an extra 5 seconds higher than before.
Her ult's mana cost got converted to flat from scaling, the only positive update to the ability since the re-work stuffed random per-rank scalings on it for her basic abilities.
What did this accomplish? Her poke and heal were straight nerfed in both base values and cooldowns, and her e took a buff for a nerf. Then her base hp was cut to 353, they gave her an extra 7 health per level with base 15 armor, and she loses 5 ms afterwards, left at 325. She basically has lower base health in the early game than a melee minion, edges into caster minion territory, receives a myriad of random nerfs called a "re-work", and somehow Sona is supposed to be "okay".
She only deals so much damage because she spends the entirety of lane spamming Q. She always did. The re-work didn't change that. And it certainly doesn't make it want to use her other abilities which have HIGHER cooldowns and higher mana costs. She's literally one of the squishiest champions in League that was converted from a stance/poke champion to a generic poke support. Any number of champions that have a hint of engage in their kits can drop onto Sona and eviscerate her. Her ult's the only cool thing about her kit and it amounts to nothing more than an AoE stun.
Nerfed across the board and only wins lanes when the enemy lets her. Of course she's garbage. Her kit needs to be redesigned entirely to actually fit her music/stance thematic while not being absolutely gutted.