Poppy's W doesn't efficiently work

Hey guys, apparently this is the best place to post this and I've been wondering what the reasoning was behind this, mechanically and logically (both of which doesn't make sense). I'll get into it momentarily,

So for Poppy's W you're supposed to bump units and they knock up right? This is neat for champs with dashes and yada yada yada, problem is it doesn't work EXACTLY like it should.

See for champs like Riven and Lucian, the bump works perfectly, even for Tristana and Bard's portal. But I learned that some heroes seem like they don't care. My key examples, and reasoning behind this post, are Fiora and Hecarim. Although Hecarim and Fiora bump when they respectively speed up and kick, or dash. Their damages and spells register; Hecarim will still damage and kick Poppy in the direction he wants, and Fiora will still stab through and damage.

As I said, if the whole mechanism is the prevent enemy dashes, and logically, knocking up Fiora and Hecarim should not enable them to hurt or kick back, think of it like Riven completing her attack as an example.

Thanks for reading