Its a nerf if you hit with Charm
Its a buff if you don't
In both cases the damage difference is around 100
Overall its a pretty big buff and it makes it even more mindless to play, since before you actually needed an slight amount of skill to hit your charm before you could burst
It's also doubtful she really needs this buff, yea she was hit hard after DFG being removed. However her main strength was never her burst, but her reliability and mobility. She has great amounts of lane healing and mobility.
There are plenty of other AP mages that need love before her
It is likely that her played amount would hardly even drop much even with the nerfs and without compensation buffs
However Riot would need to nerf Fizz, Yasuo and Zed more to lower their current dominance of mid lane