The Summon Aery rune is way too strong, and it's being nerfed in the next patch
Runes Reforged is in full swing—it's been an entire week since the new rune system went live, and players are figuring out exactly which ones are better than the rest.
Summon Aery fits the OP bill, and it's had complete domination over the Sorcery rune path, and that's exactly why it's being nerfed in the next patch, according to the latest PBE update.
Aery the fairy is a little helper that flies at your enemies when you damage them, dealing bonus damage, or zips over to your allies when you shield them to strengthen their shields, making her a very versatile little bugger. Unfortunately, though, she's so useful and reliable that mages are choosing her rune over the likes of Arcane Comet, even when Arcane Comet was specifically designed to work well with their kit.
Likewise, damage dealers like Jhin and Pantheon are even running Aery because it helps their lane harass so much, making Aery one of the most popular runes in the game. Rather than buffing up other runes around Aery to make them a little more attractive, Riot is nerfing the poor little fairy instead.
In the game right now, Aery's damage to enemies begins at 20 per tick and scales up to 60 as you level up. After the nerf, it will start out at 15 damage and scale up to 40—significantly less damage than before at each level.
Aery's power on enchanting supports like Janna and Lulu will remain, as her shield strength isn't being lowered at all, but damage dealers will find her considerably less powerful, and they'll therefore choose her less in their rune builds.
If this change makes it through PBE testing and into the live game, it will probably ship with next week's patch.