When I first started playing Nami, my opinion of her was "a better Sona." I mean, let's just compare and contrast what the two offer:
Nami:
- (Skillshot) 1.5 second stun (skillshot).
- Combination heal/poke which bounces up to 3 times (2 heals + 1 poke, 1 poke + 2 heals).
- 6 second/3 basic attack ally AA steroid (25/40/55/70/85 [+20% AP]) plus 1 second slow (15/20/25/30/35% [+(5% AP)%]).
- (Skillshot) Massive (but slow-moving) combination knock-up/slow (50/60/70% for 2-4 seconds).
- Ally MS buff on all abilities (targeted).
Sona:
- 2 enemy poke.
- 1 target heal (non-targetable).
- 1.5 second 20% AP shield (only if inside aura).
- 3 second single-target enemy de-buff (-20% damage).
- MS boost for self and all nearby allies.
- (Skillshot) Thin (but fast-moving) 1.5 second stun.
Basically, Sona is like if you took Nami, dumbed her kit down through removing skillshots and making her previously interactive abilities automatic, nerfed her stats to balance her out (Riot's philosophy: the easier a champion is to play, the weaker their abilities have to be), reduced her CC and utility, and tossed her a bone with extra damage output to keep it from seeming like a complete nerf.
Sona was the first support I found that I liked and was decent with. Having now learned, and excelled, with Nami, though, I see literally no reason to bother with Sona again. My friend, who I often support for, suggested her and I told him I'd rather devote my time to other, more mechanically challenging supports that offer more and will always be the preferred, better choice (assuming equal skill with them).
Her face-roll status is perfect for players just learning the role, as her kit plays out like a semi-interactive poke/sustain support tutorial. You can choose when you want to heal, for instance, but she prioritizes the ally with the least HP for you. You learn when to poke without needing to practice landing the skillshots most other supports will require to land that poke. And the one skillshot you have, while thin, is instantaneous, meaning the enemy has less time to dodge and the skillshot is actually somewhat easier to land. Then, the more you use her ult, and the better you get at it (ex. hitting multiple enemies), the easier other skillshots will come for you because you'll have been eased into the basics of landing skillshots: aim and prediction.
But that's all she is, and probably all she'll ever be: a safe, easy learner champion. Every role has to have one. ADC has Caitlyn, with her range and CC. Jungle has Warwick, with his seemingly limitless sustain in the jungle and gank button. Top has Nasus, with his stacks that give you a strong incentive to focus heavily upon farming, which is vital for top lane. Mid has Malzahar, with his E giving mana regen, as well as letting you AFK farm, his immobility forcing you to learn how to play safe and to deal damage while avoiding taking any yourself, and his ult being one of the strongest in the game. And all of these champions would just become over-powered if you tried to buff them because of how simple they are. We saw what happened not too long ago with Warwick, for example.
That all being said, I'm in favor of Sona getting a little love, since I've barely seen her since the DJ Sona hype fell off, and since these Nami buffs just make her weaknesses that much more glaring. I mean, the "learner" champions I listed for the other roles are also recognized as strong picks, whereas I don't think Sona would see _any _ play if she weren't so damned easy. To me, she's the support equivalent of Garen (as he was before the rework). A terror if you get ahead, but easily countered and played around, as well as lacking in utility. Buffing her too much would make her the terror of bot lane, but she needs something.