Rylai's Bugged on Ziggs E

I've already submitted a bug about Ziggs' passive and I found another one using Rylai's.

I realize slows don't stack but it is still supposed to choose the bigger slow when there's an option. Instead, Ziggs' E takes the slow of the ability even when it's lower than the 40% slow of Rylai's.

BTW: I think Ziggs needs a bit of help and I'd buff his W ratio since it's on such a long CD and so critical to his safety. This would be a very reasonable and safe buff with basically zero chance of making him overpowered. It would however, open up more windows to be aggressive late game if it was a 50% ratio instead of 35%.

Alternatively, I'd consider making his passive proc spell effects but this is a much scarier change and could be problematic with Rylai's, Luden's and Liandry's applying so it's likely that something else would need to be nerfed in some way to pull it off. On the other hand, applying spell effects would be cool and the extra power from it wouldn't be available until 3+ items. It would certainly buff his late game, which I think is lacking, especially considering that he doesn't have kill pressure early to snowball either and his damage isn't reliable.