My teammate is a die-hard Willo main and she's been absolutely DOMINATING Onslaught with her at the moment. I personally think Willo is in a great spot too, I wouldn't say Blastflower is OP, it requires you to use it right and know where your shots are going. For Willo to keep up with other high burst champs, it's clear she needs something like this to stay viable.
I respect that it does feel quite strong, but think back to the last time Cassie killed you: how many shots did she fire within a second?
Same with Lian: Eminence? Was she using Eminence with the CDR?
For Willo to be taken down on one Talent, just as she became seen as good again, we'd also have to be seeing others falling down from their extreme damage.
I would not say that my suggestion is a nerf, but a readjustment, some things were taken and some given in my post, to get to the balance point.