Alright, just tested Yi's E in combination with Rylai's. Of course you are never going to build something like that, but Yi's E doesn't apply it. Even though it is not a permanent passive and an active.
Looking at it now, it would probably have made more sense to test the whole thing with Fizz' W instead of Yi's E, because that makes more sense. Maybe I'm going to do that tomorrow.
Point is, this is not about balance, I'm caring more about inconsistency and the unreliability of tooltips and definitions and how confusing it all is.
For example - I played a Teemo game some weeks ago where I was deciding between Thunderlords and Deathfire Touch. I went for Deathfire Touch, thinking that his E would proc it, because its tooltip says and I quote: "Your damaging abilities cause enemy champions to take magic damage over 4 seconds." Teemo's E is one of his damaging abilities, so it just makes sense that it would proc it. I'm not mad because I think Teemo would need this as a buff or something, I'm just mad because the game gave me information that was just straight out not true.
I just want to look an ability or an item and it's description and be sure about what it does - I don't want to test the whole thing in a custom game first, where I have to farm 5 minutes against bots to get the item I want to test.
I thought that was just a single case but lately I'm running into unreliable tooltips and wording pretty frequently when I'm making one of my builds. One of these cases was the one I made this post about.