I know the common wisdom that every champion is viable in any position (for the most part) so long as you know what you're doing, but I think I missed the reason Kha'Zix fell out of popularity in solo lanes.
AyRe CoNteMpT3 voteshe isnt very popular in LCS right now because reasons. and since noobs always copy LCS and 99% of the community are noobs, there you go.
Cancer Dancer1 votesWith the copy/paste of the pros aside, assassins in general have fallen out of favor. You don't see many Zed/LB/ mid lane fizz/Kha because they're completely reliant on blowing somebody up and getting out or finding picks in the jungle which is harder to do with this teamfight/tank meta that we're currently playing in.
AyRe CoNteMpT1 votesthat isnt LCS-copying aside, thats exactly LCS copying. "teamfight meta", "tank meta", "reliant on XYZ"
if you want, you can play khazix and find way to make him work against whatever champs and comp you are playing and whatever your team needs.
khazix is pretty good as he can do many different things and buy many different items. i think he should be one of the easiest champions to play successfully right now.
Poptart Evelynn1 votesthat isnt LCS-copying aside, thats exactly LCS copying. "teamfight meta", "tank meta", "reliant on XYZ"
if you want, you can play khazix and find way to make him work against whatever champs and comp you are playing and whatever your team needs.
khazix is pretty good as he can do many different things and buy many different items. i think he should be one of the easiest champions to play successfully right now.
Just my own opinion but I'm decaying out of Diamond from not even playing ranked atm (because my style of gameplay is nerfed into the ground currently) so it could have shifted in the last two months.
AyRe CoNteMpT1 votesif your "style" has been nerfed, it means it was a shitty style, or even no style at all and just abusing some overtuned power. you probably are just not a very versatile player while khazix is a very versatile champion.
44400862_DEL2 voteskhazix was a solo laner when hes poke was hes burst (think zed or talon even if they need to be melee for a proper burst they max ranged spells first) riot though nah nah nah khazix damage is hes q when evoled so they took a shit ton of damage from w and threw it on q this pretty much killed mid khazix but due to this buff to hes 2 second cd q top khazix became a thing and then riot was like... welp... hes one shoting the island lane... we need to sort this out then he went threw a blender of nerfs chances and buff and we get this. a alright khazix who suited well for being a jungle assassin only problem is jungle assassins arnt really in vs this tank meta but vs stuff like nidalee jungle khazix will easily win that match up with hes isolation and just flat out faster burst. hope this explains alot
MrBuffington1 votesAhhhh right, I forgot they gutted his W, thanks
EndlessSorcerer2 votesI believe the reason he was removed from lanes was due to the changes to his Q. Not only it is far more difficult to isolate a target, you no longer get execute damage for using your evolved Q.
He used to use his Q and it's execute damage to steadily chunk down his lane opponents, but now he doesn't get any bonus damage if they are near their minions which hinders his trading potential.
MrBuffington1 votesI see, thanks!
Mat7itan1 votesAssassins have fallen out of favor because they do not do well against tanks (we are in a pretty tank heavy meta), and kha'zix in general is not played often anymore (especially in a solo lane) because the isolation range on his Q (which is most of his damage) was greatly increased making it much harder to isolate the enemy champion.
BeatzBoyFTW1 votesAssassins have fallen out of favor because they do not do well against tanks (we are in a pretty tank heavy meta), and kha'zix in general is not played often anymore (especially in a solo lane) because the isolation range on his Q (which is most of his damage) was greatly increased making it much harder to isolate the enemy champion.
Uhh his isolation radius got reduced from 500 to 425. That's not a nerf.
Mat7itan2 votesOh well that's good. I did not remember seeing that. I do remember it getting increased though.
BlacksSmokeCrack1 votesUhh his isolation radius got reduced from 500 to 425. That's not a nerf.
When you put the entirety of his damage into his isolated Q then an isolation reduction is not a nerf, it's a gut.
Sxli1 votesThe isolation radius is the distance that enemy champs have to stand within near other enemy champs for them to be considered "isolated" before it was 500 radius (bigger circle) to 425 (smaller circle) so now is easier to get targets to be considered isolated.
Only Play Darius1 votesAssassins have fallen out of favor because they do not do well against tanks
He builds 
and has on-hit true damage. He can 1v1 literally any tank in the game and come out without losing any hp.
Best Darius KR1 votesMaster Yi is a fighter, not an assassin
44400862_DEL1 votes[{quoted}](name=Jelly Mac,realm=NA,application-id=WEuoGbmp,discussion-id=glh7gunm,comment-id=00030001,timestamp=2015-06-28T03:30:39.977+0000)
He builds
Rammus with thornmail, have fun yi
Hasztalan21 votesThe main reason why he sucks in lane is the same as 
and the likes, he has too many losing matchups and incredibly feast or famine, meaning if he gets a kill he instnatly goes 10-0 , if he dies early on 0-10 is plausible. And he has no fallback pattern since as laner you cant just abandon ur lane and go into the jungle.
George LS1 votesbecause his only way of sustaining the lane is also his only way of csing-harasing from distance , even mele meta midlaners/tops like Diana and rumple have enough range harras to punish kha zix each time he tries to come in for a cs .