What is the purpose of the Sion changes on PBE?

Obviously this is an attempt to nerf Sion in a way that doesn't effect his q max playstyle much, but this is almost strictly a nerf to Sion in all his builds. The bonus 10 damage on q doesn't even come close to making up for a loss of 25% ad ratio, which is lower overall now even at max rank.

If this is an attempt at a straight nerf, it's very strange, and if it's supposed to not effect q max Sion, it doesn't seem to do its job very well.

I don't see the point in these changes.