I honestly don't see that much of a reason to nerf 
. Support wise I believe she's fine with her Tormented Soil. But I can see and agree with others that Dark Binding's root has too long of a root. At full level the Champion is root for three whole seconds. 
's Q is only a second long and even his ultimate is two.
Morgana is being nerfed because some LCS Thresh main asked for it.
Every season, Riot leaves Thresh and Leona atop support the class and then wonders why Morgana sees success there...
The whole point of putting Morgana in a solo lane is her ability to safely farm. She doesn't have anywhere near the kill potential in-lane that other AP Mids have, why is it suddenly a problem that she can farm well?
Why are so many people bitching about Dark Binding when there's Death Sentence and Power Grab? Her Q IS vital to her playstyle because most of her kit's damage relies on enemies standing in one area for an extended period of time.
Why are people are still bitching about Morgana when Thresh is allowed to completely dominate the support role since his release?
If I had to guess, it's probably for a similar reason Lissandra was nerfed; they want her to have to put more effort into her waveclear, specifically for top lane. Kind of sucks for mid lane Morg, though; I was playing her in PBE, it's still manageable but noticeably more difficult to shove a wave. It'd be nice if they bumped her AA range up to like 475 or something to compensate, since she has to use more autos now.
The question isn't why she is nerfed, the question is why her W is nerfed, which is the least problematic art of her kit. 3sec snare on 1300 range? why not, thats the longest hard cc besides ashes ult just on a normal skil... A massive anti magic shield that grants CC-IMUNITY, no problem, olaf needs his ult for that and looses def-stats instead of gaining a shiled but who cares...
Morgana needs a bigger rework, sheÄs a relic of the past and honestly fits better into dota than into lol. But till that time comes, they could atleast lower the snare duration to 2 sec, lower the cd on higher ranks to 11-9, let W deal the same damage over 4 sec and if needed even reduce the ult leash from 3 to 2.5 sec. This would buff ap-morg as she wouldn't rely as heavily on the Q, and it would make her less hit or miss as the Q has less impact but also less downtime.
I don't think it's focused on "support" Morgana. If Morgana builds full support "
then she's not too much of a problem, other than her moderate damage and strong possible crowd control.
The real problem starts when she builds full ap, and her full combo is nearly 2100 to a single target, and 300-900 damage to each person in a group.
I talked with my personal friend who has played since Season 3, he said Morgana is overpowered but not at the same time. She's totally reliant on her Q to deal damage and be effective, yet that Q does so much damage, and the root duration is absolutely ridiculous. I think the nerfs are necessary but they didn't do it properly. Honestly her W could use a buff but her Q needs a heavy root duration nerf. This is mainly because you can go 30/0 but as soon as the enemy team finally lands a Morgana root then it's gg for you. It's so easy to hit and does a ton of damage.
It's hard to say a champion is overpowered because one of their abilities are while the rest are okay and balanced but it was like the old Nidalee, the one time you didn't dodge her spears then you instantly died.
She's being nerfed because of Morgana Top LCS. She's able to farm too safely to Riot. This is a huge nerf to Mid Morgana which I love, and it's a shame that 1v2 Morgana in LCS that will never be played in non competitive games is nerfing the whole champion extremely hard. At least buff her range to like 500-550. How the hell is she supposed to farm if she can't clear a wave and she has to auto at 450 range?
Riot doesn't care what you guys think. They don't care that her Q duration should be nerfed. This is a nerf purely based off of competitive play.
Morgana is too damn strong and always has been to damn strong.
I think the reason why is because in a solo lane she would be pushing lane hard by just pressing W. You got put under huge amounts of pressure and she didnt have to burn much mana while you had to just to get CS.
As a Morgana player, I'd be totally fine with them lowering her q duration if they reverted the 50 nerfs they put on her recently.
