It's all about your play style. I agree that Sona is ineffective if you're trying to play her as a carry, she doesn't have the burst damage or ability to create and take kills. Any Sona that is getting tons of kills a game is stealing kills from carries who could make much better use of that gold than Sona can.
That being said, there are weaker champs and stronger champs in the game, but every champ is viable. Just because Sona isn't really the most viable champ to carry with, and should be considered as a support, doesn't mean she needs to be a helpless support.
The playstyle and build i'm talking about in this guide advocates a support sona, just... an aggressive support. If that makes sense.
Something like solo sona, while a viable option, obviously isn't the best choice, or necessarily a good one. Just because something is possible, doesn't mean it's a good choice, simply because she isn't a great carry, and the way I explain how to do it in that part of the guide is neither a good playstyle, or the most effective. It's just possible.

I guess the bottom line is, I advocate a very aggressive support, because Sona doesn't have the damage or abilities to make her anything else. An aggressive support sona > pure support, if that makes sense. :)

SolWP18 - I was reading over on the LoL forums and they have a recent thread about Sona and almost to man, so to speak, they have stated that Support Sona is much more viable than AP Sona especially after the nerfing. Space does not permit me to give their positioning but the bottom line is Support Sona > than AP Sona.

Your thoughts?

Thanks! Glad someone liked and found it helpful!

Really like your Playing A Support and The Bottom Line section; well thought out and instructive. In fact, the guide as a whole is well done. My son just played a Bot game to try her out and he found her a lot of fun.