All 4 of Kha'Zix's evolutions should be equally viable

Right now, his Q and E are pretty much necessary to assassinate people and then escape. And his R is pretty much garbage now so you just take W unless you want your R purely for aesthetic reason.

There should really be a choice in evolving, considering he is supposed to adapt to the situation, which right now the only things changed are whether you take E first for early dives or Q for early damage.

For the most part I feel like is one of the more healthy assassins we have, who is both fun to play as and against; Isolation=kill, no isolation=no kill. But his evolved R seems pretty pointless right now. Previously we had the damage reduction, which obviously was a problem back when Kha could jump W in air to slow and Q you under tower, then R to receive 50% damage reduction.

A thought: What if evolving R made it so towers were no longer considered allies for isolation? Or perhaps even evolving it could even allow you to now W mid Leap, or gave your E something (couldn't think of something for this). The reasoning behind this is, his ultimate should feel more ultimate if you evolve it, now just give one more proc of your passive.

Of course, if his evolved R were to interact with his other evolutions this would mean it could also only be able to evolved at level 16.

TL;DR: What if ultimate was only available at 16 but made his other evolutions better in some way.