I've always thought of Sona as being a strong bully and worthless late game but the winrate by game length chart shows the opposite. It shows she has about 37% win rate at 15 minutes then a steady climb to 55% at 35 minute before spiking up to 67% win rate at 45 minutes. What about her would cause this when she seems to me to be a bully who falls off just from my experience playing against her.
O Fallen Scholar1 votesShe just spams everything late game. Early mid u can't really spam.
greekvandaL1 votesCause she is the same thing as in Urf by lvl 16.
Dancing Foxx1 votesGroup shields every few seconds late game. Helpful when buffed by ardent and redemption.
Kaioko1 votesShe's not a lane bully whatsoever anymore with how much healing you can reduce from poke champs (Fleet Footwork is used on nearly everyone). Her late game is amazing with how much she can spam her abilities and the low cooldown she has thanks to the ultimate passive. With the combination of that and and ardent censor you can essentially eternally buff your whole team the entire duration of a teamfight.
SEKAI1 votesBecause in late game it's mostly about teamfights, and Sona is incredibly good at those, especially when late game she now has a bunch of support items like the Locket, Redemption, Ardent, etc that make her do even better in them.
Not to mention, any Sona with more than 2 brain cells won't miss her ulti (though choosing the best situation to blow it might be tricky). And her ulti literally wins the late game as soon as it lands.
Relia Fortune1 votesHer Aura spams on W give massive shields late. 
is so strong on her.
She honestly needs a few items to get going, as she is rather weak early imo. Definitely gets stronger as the game progresses.
Azadethe1 votesHer win rate is reliant on how far into her R she gets, because it offers a passive that multiplies against CDR on her normal abilities which cause late game sona to be a different animal.
You can get 10/25/40% additonal CDR reducton per Ult tier. At 40% + 40% her basic heal at tier 5 = 2.16 seconds at level 16, and at level 11 it's only 2.7 seconds, and at level 6 (assuming 40% cdr) only 3.24
Her Q has an even lower cooldown, etc.
Furthermore, late game she starts moving her teams really fast with E.
If you build and focus active items on Q, you're going to fall off. You really need to go AP instead, and focus W to have a viable mid-late game.
If I can get to 3 full items, I've pretty much won the game:
AlienPrimate1 votesI never knew the passive part of her ult existed. It makes sense to me now that her win rate would jump up upon reaching level 16.
RedCyclone1 votesSona is one of the hardest scaling AP champions out there, she is basically the support equivalent of Nasus Vayne in terms of stopping power
With fullbuild (subbing boots for deathcap) she probably outputs more then any other champion in the game, the only issue is getting there due to that she is a support and a fullbuild is unreasonable for any game that hasn't lasted a hour, I rarely get past 3 items with her now and games are usually over before I get to have fun with lots of AP