I think you missed the reason why they're reverting Kog'Maw. It's not because people didn't like it - in fact a lot of people enjoy this Kog'Maw.
It's because the changes didn't accomplish the goal. They wanted Kog'Maw to be a team-annihilating lategame hyper carry. Instead, he became a team-annihilating midgame monster that was also good lategame. More specifically, the ideal itemization for the current Kog'Maw gives him a ridiculous amount of midgame power. This is actually a case where the items made a champion broken and Riot actually changes the champion, not the item.
Honestly, it was rather evident that Kog'Maw's power was not functioning as intended. The guy who is supposed to be a hyper carry should not stat check me in melee range at level 11. Personally, I think they could have tried some changes without reverting his W, but I understand their decision.
In Malzahar's case, the rework is serving its purpose. They wanted Malzahar to keep his focus on locking down enemies, but emphasize voidlings as a key part of his kit, not just extra damage, something many Malzahar players had been asking for. They wanted to give him more of a gameplay paradigm than flash-comboing someone who then dies during the CC. His Q has a higher uptime on the silence and does more DPS, rewarding Malzahar players who consistently landed it, and punishing it as part of a 100-0 combo. His E has less damage, but can be refreshed with his ultimate and Q and his voidlings are much more of a threat. Again, this makes it so he has more damage over a period of time and less ability to 100-0 during his CC.
This focus on damage over time and continual presence is why he has his passive - one of the reasons Malzahar was so dependent on flash-comboing at the right time and getting his kill is because he had no way to defend himself aside from his combo, and was incredibly punished for even trying to position if it wasn't perfect. This is also why he was neither popular nor performing exceptionally, he was like an Annie that only stunned one person. His passive gives him room to maneuver in this era of dashes and stuns and blinks and take advantage of his lower Q CD and his powerful voidling DPS.
I honestly don't understand the hatred of Malzahar's passive, it fits really well with his kit and his theme. Considering how often I see people use major abilites when they can see its up and have their CC or damage absorbed, I'm inclined to believe it's just salty aggromaniacs who can't imagine a situation where mashing all their buttons doesn't get them a kill.
Saying that his kit is gutted because of his passive is ridiculous. His potential voidling DPS is insane, his Q has a 3.6 second cooldown with full CDR, meaning you can theoretically keep E on something forever. His ideal realistic scenario involves having E on multiple people for an extended period of time between bounces and refreshes while his voidlings. If you think his kit is gutted, it's because his playstyle has changed and you aren't adapting.
The fact is the rework turned Malzahar from a mostly irrelevant niche one-trick-pony champion with mediocre performance into (after the balancing) a more versatile control mage who can wear down an entire team from relative safety if left unharrassed. He became more popular, performed better, and was able to do more as a champion. When I play against a Malzahar now, I have to be much more concerned about his silence and his voidlings. Before, all you did to fight Malzahar was wait until he stunned himself with his ultimate and then blow him up. This is exactly what RIot wanted - they wanted fighting Malzahar to be more engaging for both the Malzahar and the person fighting him.
The point of the Malzahar rework wasn't to appease you or whatever group of friends helps echo your opinions, it was to make him a more interesting champion. In this regard, succeeded. Specifically, each of his new abilities served their purpose. His Q became a more active tool, rewarding skilled players and giving him more zoning potential. His E serves the purpose of rewarding his other skills - it gets extended with Q and R and makes his W voidlings focus a target. His R gives him the trademark suppression and can be used to ensure voidling spawns by allowing them to attack. His passive gives him room to do this without dying because someone looked at him funny, and makes it so he doesn't instantly get targetted when he ults. All of these abilities are being used in the manner they intended, and Malzahar is serving the role they intended at the power level they intended.
This isn't the case for Kog'Maw. Kog'Maw's winrate is strong for the entire game and is spiking midgame. Furthermore, his inability to stutter-step while using W means the ability has to be insanely powerful for him to work. This is a case where the idea is fundamentally not working as they intended. They're not changing Kog'Maw because some people on the forums said they didn't like it. They're changing it because the ability is turning the champion into something it's not supposed to be.
TL;DR Riot isn't changing Kog'Maw because of what you, or anyone else, likes or doesn't like. They're changing Kog'Maw because the reworked ability is essentially serving the opposite of its intended purpose. None of Malzahar's abilities are this unfortunate.
