I mean, that's always been Rito's attitude, both towards champion balance in general and also towards Sona specifically.
Rito has this distinct problem where they refuse to nerf the problem points of a champion. They believe repeatedly cutting around the problem, over-gutting every other aspect of a character will somehow miraculously make "weak points" for enemies to exploit. It has never worked, in the end they always finally have to resort to nerfing that problem point, but then they blatantly refuse to revert any of the nth previous nerfs, leaving the character OVER-nerfed. It happened to Lucian, it happened to Yasuo, it happened to Sejuani, it's happening to Sona.
Speaking of, Sona's problem point isn't her damage. She already has the lowest damage of any support, the problem point is her R passive. It's the reason her first rework failed, it's the reason her 2nd rework failed harder, when they gutted her numbers even further to funnel even more of her power budget into level 16. It will never matter what her kit looks like, until Rito stop tunneling 99% of her strength into R ranks.
Furthermore, Rito is extremely wary to nerf Sona's damage any more than it already has. They know Sona has the lowest damage of the support class. They know her Q has the lowest base. They know nerfing it even more, won't reduce Sheen's strength, but they did realize GUTTING her base AD matter-of-factly did gut her affinity with Spellblade. They knew her winrate would nose-dive after that nerf, they knew her winrate would nose-dive after gutting Aery, yet they already queued more Sona nerfs before that even reached Live. They knew they would eventually gut every Sorcery mastery, not because of Sona, but Meddler was allowed to use them as an excuse to gut Sona first anyways.
Now here we are, Sona is at her lowest point in the history of the game, which honestly doesn't even mean much, since she has only ever gone downhill since the beginning of League regardless. She's never received a buff, she's received nerfs every season since 3 and she hasn't existed in professional play since her first rework was just a list of some 30+ simultaneous nerfs and like 1 sole "compensation buff," which still nets a grand total of neg 30+ overall changes in that one patch alone.
Also, since Sona's entire power budget is funneled into level-16 URF-mode, every single nerf she receives that doesn't include the text: "R-passive removed" is essentially two nerfs in 1. She gets a nerf to her early game, her laning phase where she's SUPPOSED to be strong and also a nerf to that non-existent late-game fantasy, where her machine-gun of shooting pathetic air-soft rounds gets multiplicatively weaker by shredding power off every single of her 5-billion casts. A direct result of her failed 2nd rework.
