Sona slammed with nerfs and underperforming tanks were buffed in yesterday's micropatch
The preseason patch—the largest update of the year—went live last week in League of Legends, and oddly enough, it's been mostly balanced except for a few champions.
Some of those champions are Sona, Ornn, Ivern, and Nunu, and they were all addressed in a micropatch yesterday.
Most champions were strengthened by the complex new rune system introduced in last week's patch, and it even opened up new and off-meta strategies to be viable for the first time. Unfortunately, Ornn, Ivern, and Nunu didn't benefit much from the new runes, simply because there isn't a Keystone rune that belongs in their builds.
Of course, there are some Keystones that work on them, but they don't get much from Aftershock or Grasp of the Undying, and certainly not the Sorcery or Domination pages. They're limited to either the Inspiration path or runes that only work in niche scenarios, like Aery.
In the micropatch, none of the runes were changed to suit them better, but they were buffed, at least. Ornn's Searing Charge damage was raised at all ranks for both the initial damage and shockwave damage. Nunu's base health was raised from 540 to 590, and Ivern's Triggerseed shields for more at all ranks. This should help these tanks perform a bit better, but if they want to find long-term viability, the runes will need some work as well.
Sona, on the other hand, was way too powerful. This is because almost every rune path works for her in some way, with Electrocute on Domination, Aery and Meteor on Sorcery, Kleptomancy on Inspiration, and yes, even the Resolve path with Guardian. Having so many optimal builds has turned Sona into quite the powerhouse, so Riot nerfed her base AD and armor, as well as the heal and shield of her Aria of Perseverance.
The next patch won't be here for at least another week, but it's safe to assume that these champions may need some followup work.