[{quoted}](name=A Vitriolic Cat,realm=NA,application-id=3ErqAdtq,discussion-id=Ab1sfOlt,comment-id=0000000100010000000000010000,timestamp=2015-11-27T07:14:08.468+0000)
Okay, let's look at this setup though. Nami's teamfight ultimate is much harder to use in a lot of scenarios then Sona's (since it moves much slower but has longer range this is mostly arguable, but I feel like there's a lot more counterplay to dodging it). Nami's kit is also not that of an aura/sustain support as much as it is a skirmishing support - she DOES have a heal but healing is definitely not the brunt of her kit. She's intended to fight the enemy laner, using the heal as a health swing during a skirmish (since it bounces around dealing damage and heals). These things work together.
Braum and Leona we won't even talk about (I NEVER SAID SUPPORTS CAN'T HAVE WOMBO/TEAMFIGHT ULTIMATES, but that it doesn't fit on an AURA/SUSTAIN support like Sona, which none of the champs you listed are).
Currently Sona has a kit that favors short trades with breaks in between to heal back up, looking for good opportunities to counter an opponent moving out of position. She does well in teamfights (even with just QWE) by giving her auras to her team and providing shields, healing, and some damage amp in the form of Q procs for her team. And then she has a random AoE 1.5 second stun. Her kit (which is great for sieging minus the ultimate) has a random huge teamfight CD attached to it. On someone like Nami it makes more sense - she has her Q, it combos together into her R, but her healing is much weaker than Sona's and she doesn't offer quite the same amount of teamwide utility (yeah she gives movespeed, but Sona does too and hers is easier to utilize on a wider range of people, barring Nami's ultimate). I really, really wish that Sona had a permutation of a Karma ultimate, either where you entered a state where your auras were empowered and your spells worked differently for -x- amount of seconds, preserving her aura/sustain feel while giving her a clear increase in power for those clutch teamfight plays - or they gave her an evolving ability mechanic with her ult instead of the current flat buff to everything for each rank in ult. Allow Sona some decision making while removing some of the hidden power from her kit, and she suddenly becomes much less oppressive to play against. People complain a lot about Sona but I feel like she's way less annoying to lane against than Soraka with the caveat that Soraka doesn't have a big AoE stun as her ult.
There are so many points of this that i either just disagree or would claim you are just wrong about. She is not a good siege champion, her abilities other then her passive have no effect buildings. Her heal is really lack luster, lacking the base numbers to really do much of anything to help your team mate until you are rolling in the late game with 200-400 AP.
Also Sona has moved so far away from the old aura sustain build that it's more or less pointless to even mention it now. Her current kit is not aura's it's a thrown together chimera of one time bonuses, many of which don't last long enough to see full effect.
It always amuses me that people complain about Sona, she is actually super easy to play against if you can even remotely pick up your opponents pattern. So much of Sona's damage is based off your opponents letting you get in free hits. It is very rare that the creep wave is going to be in a place where Sona can land her Q into AA without being open to counter poke or getting caught by an ability. Late game a ton of her power simply comes from building a ton of inflated damage. One doesn't complain when the Ziggs with
and 300-600 AP is auto attacking for metric tons of damage, so why is it an issue when Sona does it?
While we are talking about her ultimate though, what do you think would be a good replacement? Because as Sona stands it's basically 40-70% of her reason for existing in the late game. Remember that without a damage ability for an ultimate she has 1 offensive based skill, while still being one of the most fragile champions in the game. Also remember that without the stun part of her ultimate, she is the only support without a built in form of CC. Hell even Soraka has a built in root AND slow in her basic kit. Sona has to use her passive to even get a slow.