In support's case specifically, this is a bigger issue because Soraka and Sona are built on shaky design foundations to begin with. On the flip side, both have a pretty loyal fanbase who enjoy those playstyles and get really angry about changes to them - even if the game or character would get better as a result.
I agree with your analysis that Soraka (and likely Sona) will always be either flattened out, lackluster or must-picks with their current core designs - do we change those and let their power shine more? Do we nerf core mechanics to be balanced and remove fun from the players who do like them? We have done this before, and I think our ability to do so today is much better, but it's always risky and a tough decision.
It's always boggled my mind that you guys have not done some of the following changes considering you've often said you felt she was toxic to the game.
Increased Starcalls Range
Reworked Starcall into a Target-able AoE Spell. ( Similar to Lux's Lucent Singularity )
Increased Starcalls Damage
Reduced its AoE Radius
Increased its cooldown
Reduce its Ap Ratio
2: Astral Blessing
Remove the armor buff.
Reduce the amount of health recovered.
Reduced the cool down.
DRASTICALLY Reduced the mana cost.
Make it heal a base amount and then so much over time.
Increase its base damage.
Give it mana cost on enemy cast.
Reduce its ap ratio
Give it a 2 Second Channel Time.
Make it apply Astral Blessing's armor bonus to all allies DURING the channel time and then heal all allies after the channeling has finished.
Increase it's base healing amount.
Reduce its Ap Ratio.
I mean, some of this may need tweaked but it seems like a logical step in fixing her from passivity and massive heal dependency. It however also allows her to still feel like a healer ( Which I love about her ) without completely making her useless.
I feel changes like this would also make Wish more of a "Lets initiate a team fight" instead of an "Oh ****, everyone's going to die" spell. Helping to alleviate the negative feeling she imposes on the enemy team when it comes to escaping ganks or preventing those near death kills.
Her ultimate would feel more satisfying due to the larger health recovered. Making it truly feel like an ultimate. However her over-all healing throughout the game would be reduced due to the Astral Blessing nerfs. I feel this would cause her to be less "Annoying" during the laning phase but allow her to be useful during late game as well.
I don't mind her healing ratios going down and being reworked into a more active champion. I just want to see real changes to the way her abilities work and not just number tweaks. There is a reason Starcall is not used among support Soraka's and it's not because of its damage...it's because the spells implementation is terrible.