Update: Another hotfix for Janna has just launched! She was still too strong and now her Tailwind passive gives her much less magic damage and her Eye of the Storm shield is even smaller.
Passive - Tailwind percent of bonus movement speed dealt as magic damage reduced at early levels from 35% ⇒ 15/25/25% at levels 1/7/13
E - Eye of the Storm shield decreased from 80/120/160/200/240 ⇒70/105/140/175/210
7.19 may have only hit earlier this morning, but Janna has already gotten some post-patch changes. Everyone’s favorite windy support was one of 7.19’s major focuses and I guess they ended up going a little too far, as Janna started the day being even more powerful than she was pre-nerf.
The hotfix was:
Base Movement Speed 335 -> 320
Base Health 525 -> 500
Base mana 409.52 -> 350
Zephyr (W) cost 40/50/60/70/80 -> 50/60/70/80/90
The nerf to all of her stats is pretty impactful here, but the most noticeable change will certainly be the increased Zephyr cost combined with the reduced base mana. Alongside these changes, which have already been released onto live servers, Riot posted a response to their forum.
Basically, this post adds context to the hotfix. Riot knew that Janna may be a bit too strong after all the changes to her and Ardent Censer went live with 7.19. As a result, they were very closely monitoring her win rate and had changes ready to go. If this is their approach to keeping Janna in line, it certainly seems possible that this will not be the last hotfix that she sees during the 7.19 cycle and I would expect even more changes to come in 7.20.