instead of making kalista scale awkwardly on AD,

She's already barely playable with all of the nerfs they've made to her passive...

She already does this.

"While dashing, her basic attack wind-up is only reduced by 0.66% per 1% bonus attack speed, rather than the standard 1%." Essentially, attack speed doesn't reduce her wind up as much as other champs, making it less effective.

You mean "lower her base AS"

Because that's functionally what you're asking. Base AS is the way that %Bonus AS scales from items and leveling up.

She's currently at a base 0.658, gaining +56.1% AS from leveling up, making her total level 18 AS 1.027 and making her hit the 2.5 AS cap with +324% bonus AS from other sources.

If it were nerfed to, say, 0.615, her innate AS would instead be 0.960 at level 18, and it would take +350% bonus AS from other sources to cap AS.

That's how it works.