Sona

She's balanced but is dominated by

Let's put it this way:

• She has the 5th-lowest base HP in the game and 2nd-lowest of support champions
• With the exception of Ezreal who has a blink, Sona is the only champ in the bottom 11 HP-wise that lacks a pre-6 snare/stun
• In general, she's the only support in the entire game that lacks CC pre-6 harder than just a slow, except for very rare off-picks
• At the same time, she also sits in the bottom 15% of champions max armor-wise and once again is the 2nd-lowest amongst support champs
• Despite being amongst the squishiest characters in the game and completely lacking meaningful CC to compensate, she also sits in the lowest tier of MS

So to summarize: She's very squishy and completely lacks compensation as a trade-off for that squishiness