Do you actually read the patch notes or changes to Sona?
or are you illiterate and require someone else to tell you? Because while she was "nerfed" in season 4, the changes weren't very impactful to Sona. She's still very viable.
Here's a list of changes to Sona ever since the rework (taken from the wiki page which documents the changes in her background page):
V5.1:
Stats
Movement speed reduced to 325 from 330.
Power Chord
Hymn of Valor's Staccato damage reduced to 40% from 50%.
5 MS is not going to impact a champion who can cast all her zero-cast time basic abilities without stopping, an aoe stun, a slow and an aoe MS buff
the damage reduction on Hymn of Valors Staccato damage is about 20 dmg lost at level 18 on an empowered Q. Before level 18, that damage lost on auto is even smaller. "Obviously we lost that teamfight because Sona, our support was short 20 damage on her Q."
V4.21:
Hymn of Valor
Should no longer cause game lag on first cast.
this is a bugfix
V4.20:
Hymn of Valor
On-hit damage AP ratio reduced to 20% from 25%.
Aria of Perseverance
Base heal increased to 30 / 50 / 70 / 90 / 110 from 25 / 45 / 65 / 85 / 105.
Heal modifier per % missing health reduced to 0.5% from 1%.
Mana cost increased to 80 / 85 / 90 / 95 /100 from 70 / 75 / 80 / 85 / 90.
The Q nerf only affects her scalings in the mid-lategame when she starts to buy rabbadons. It's not a .5 ap ratio nerf, it's a .05 ap ratio nerf. Technically it's a .25 ap ratio nerf to half of an ability with a 1.25 ap ratio (assuming you get everyone the empowered auto and they all use it, which from my experience NEVER HAPPENS).And this is nerfing the extra damage they added to her Q from her rework. It's like they give you a free machine gun and then remove 2 bullets from the magazine; in the end, you still have a free machine gun. But let's complain about the free machine gun nerf. And again there's the argument, "We lost that teamfight because our support didn't do enough damage".
W nerfs are also very small, the change only affects extended trades, and by 10 mana points per cast. The 0.5% heal modifier nerf is another extra bit that was added as a result of her rework. It's another free machine gun minus 2 bullets.
V4.17:
Hymn of Valor
Fixed a bug where the damage range was 700 instead of the intended 850.
This is actually a bugfix, that can also be though of as a consistency buff
So in actuality, she got nerfed twice. But you know, we gotta force that crappy "better nerf X" meme right? It's still funny guys right? It's still funny?
And look at those nerfs. Nerfed right into the ground, 5 MS lost, up to 20 damage lost at level 18 on her Q, W mana cost and missing health lost-
she's completely unplayable from these nerfs!
"but her rework was also a nerf"
That depends on how you look at it. Most players (by most players, I mean I've read comments on this board, on youtube and on other league of legends websites such as Surrender@20 that) agree that she's still the same aura mage as before, except the benefits of her auras are more noticeable and faster than before. She also saw a little bit of competitive play post-rework in the LCS (something that hasn't happened for Sona in a very long time).
The range of her auras (and therefore her safety) was decreased from the rework. 50% (now 60%) of the bonus damage on empowered auto attack Q was lost. She also lost her ability to help in pushes by granting AD post rework; but she has better ratios now and also better base values (assuming you use all of her Q) to make up for it ( and a lot of players including myself, like the aoe shield on her W).
Looking at the remaining Sona changes of season 4:
V4.5:
Stats
Base armor increased to 12 from 8.
armour buff?BUFFS?
V4.2:
Song of Celerity
Fixed a bug where the tooltip improperly showed a +4% per 100 AP scaling for both effects.
Fixed a bug where the haste was only using 1% of Sona's AP instead of 2%.
Fixed a bug where the slow was only using 2% of Sona's AP instead of 4%.
and some more bug fixes
So no nerfs beyond the 2 (3 if you count the rework). And the 2 were some of the smallest changes I have seen.
So yeah, Sona was definitely nerfed into the abyss alright. Keep saying that.