I'm honestly starting to think that Riot is treating Sona like Yorick.

Think about it.

Yorick was taken out of the free champ rotation because of his annoying playstyle in lane. What does he do? Spam ghouls whenever convenient. Farm in peace, and when your laner decides to get in your face, throw ghouls at him and get him to back off. He heals, he damages, and when things get really hairy, he ults.

So what does Sona do in lane? If the enemy gets to close, she throws Q out and pokes them. If her carry gets hurt, she pops W and heals the two of them. Danger inbound? Press E. REAL danger inbound? She ults.

Both of these champs can combo their abilities. Yorick gets more damage reduction for each ghoul, which encourages a spammy playstyle. Sona gets bonus effects if she combos, which encourages a spammy playstyle.

And yeah let's also not forget how obnoxious she can get when played in ARAM / URF due to less mana constraints.

So what does Riot do? Progressively nerf her over and over. They want her to maintain her identity as the musical support, but her playstyle is just as aggravating as Yorick's is. Perhaps they just want less people to actually use her, while they go about trying to think of what to do.

I wouldn't be surprised if in a month or two she gets taken out of the free rotation as well.