Suggestion for Kha'Zix's R evoutlon: Speed instead of stealth

Before I go into my idea I want to preface this with my general consensus on what Kha'Zix as a champion is, If you don't want to read this just scroll down to the balance suggestion, i'll mark it.) To me, Kha'Zix's evolutions are, at their core, divided into 4 not necessarily unique but definitely outstanding, major gameplay mechanics divided between them. Q=Offensive capability. W=Utility. E=Mobility. R=Defense.

This is how kha'zix's kit is broken up when you're looking at your evolution paths, simple enough stuff. Now, in the past, Kha'Zix has been having some difficulties becoming balanced, mostly due to either overlap (his first iteration overlapped W damage and utility for instance.) or things being too on the nose (His Q %execute, his R damage reduction. etc.)

Now, I'm a firm believer in Mobility being the defensive stats for assassins in this game. No assassin should be able to tank or sustain in-fight effectively, they should be relying on deception, flanking, and general slipperiness to drop targets without getting blown up themselves. Tanky assassins just makes them hard to deal with and just generally low counterplay champions that are fun to play but not fun to play against. Kha'Zix, to me right now, is the very epitome of healthy assassin paradigms. He has a very specific niche. if a target is out of position he's able to execute on that very swiftly. He has clearly defined weaknesses and strengths that can be exploited by the enemy team and improved by his own. His Isolation damage, while extremely, EXTREMELY powerful for a basic ability, is limited by proximity of friendly units. this leaves him to be much more exclusive in his target acquisition than say, Talon, or Zed. He's easily one of the best designed assassins in the game right now for this reason, and I personally think Riot should try to replicate this for future assassins/reworks. trying to find an assassin's niche and specific benefits and weaknesses so it isn't just an arms race between who has the best numbers at the time.

This was the problem with Kha'ZIx's evolved R at arond patch 3.16 or so. He was given an absolutely ridiculous 50% damage reduction on his ultimate for a total of 6 seconds, He was nigh unkillable while shoveling out massive amounts of damage. He was eventually nerfed for this (and rightly so) and his entire kit was changed around to, eventually, what we see today. Q evo being a huge nuke, W evo utility, and E mobility. Where does that leave his R evolution? It's pretty much benched at the moment, it gives an alright move speed boost, 6 seconds of stealth broken up into Three increments of 2 seconds, with a down time of 1 second between each cast. his evolved ultimate is simply not worth it, it doesn't give him anything compared to his other evolutions, the utility of W, the Damage of Q or the mobility of E.

Now, this is where my suggestions come in.

I said earlier that His R evo is his defensive ability, but I also said that defensive stats on assassins should be mobility/stealth. So where does that fit in for Active Camouflage? It's simple, remove the extra second per charge, and give him a monumental speed boost on his ultimate, (Think 80%, Non decaying) This will separate the mobility from his E, which is generally more offensive mobility, from the mobility granted by his R, which will generally be defensive mobility. This change allows kha'zix to play from behind by going something like Q-R-E or Q-R-W and still have that mobility, but packaged differently in the form of a speed boost. This also means that he'll never be that unstoppable freight train of damage that he was in season 3 with his evolved ultimate. If he Goes Q-E-R evos, he's got a ton of mobility and damage, but little utility, or survivability, meaning he'll have to rely on his teammates to set him up or wait for the opportunity instead of just hamming it through the team.

going W-E-R gives him utility and mobility, but not as much damage as Q evolve, leaving him to be a more defensive, cleanup style champion that can only truly engage when his team is winning.

Going Q-E-W allows him offensive mobility only and Q-R-W less extreme, but more "accessible" mobility in the terms of a far less egregious movespeed buff instead of a resetting super gapcloser in the form of the E evolution.

What do you think? would these changes push kha'zix too far over into broken territory or would it be just the right fit for a mobile bug like himself (Or would it change absolutely nothing and leave his R evo forever benched)?