Why do I enjoy Vayne but not Kalista?

This is not a Kalista QQ thread, but I was wondering both of them seem to fit into that hyper mobile damage dealer niche so why I do find Vayne so goddamn fun to play but Kalista so lackluster and dull?

Secondly, am I the only one who thinks Kali's default skin (classic Kalista/no skin) looks bloody awful? Those ghostly spears don't look like dangerous weapons from a demonic realm, but rather some sort of glitch or video card malfunction, her walk makes her look like an ape and her armour just looks like something a peasant salvaged after a battle