I think you're sacrificing readability for motion in your art.
Or, to put it more simply, in an attempt to make your splashes look cool, you make it so it takes me a couple of seconds to figure out what the hell I'm looking at. Kat's art is the most obvious, but most of the new default splashes have this problem. I know, I know, it's supposed to look action-y and dramatic, but it really just seems sloppy and just not thought out very well. You're trying to sell people on your champions with splash art; it doesn't make much sense to have to make someone look at the splash for a couple of seconds before they can figure out what's even going on. 'Is that her knee? What the hell is going on with her legs? Is this some sort of assassin? I'm confused.'