But thats a problem that want to play a dedicated healer type style. Out right nerfing her healing will make a playstyle more difficult and therefore less useful. Her heal is only really a problem come late game where the sona team can get in and disengage allowing themselves to top off. In a serious fight it isnt that hard for many dedicated dmg dealers to out dmg her healing. Especially if the team buys the anti healing item like they are supposed to against a dedicated healer champ.
I understand also that changing her q to be a buff to allies verse direct damage would also be a drastic change to a playstyle. So now we have the problem of Riot not wanting supports to be too heavy on poke and damage, and riot not wanting supports to be able to heal pretty much at all (I'm exagerating but only a little. Riot is ona crusade to ruin healing in game)
So it comes down to picking one or the other and changing it in a meaningful way as to remove the "unfun" aspect of playing against her. More people complain about the Q auto target and power chord follow up being too strong so changing that to be different seems like the way to make the largest number of people happy.
Yes it will piss players off but so would W change. At this point there is no right answer to changing Sona to make her fun for everyone foe and player alike.
Sorry for the long post.
(Also personal feels are that tbe 4.13 patch ruined Sona. She was the most fun to play back then and not too many people really seemed to struggle against her but oh well. Riot never goes back on a rework even if it would be for the best.)