I, personally, am not fond of the Gero idea. But the gravity chamber? Sign me up!)
Not sure why you don't like it, even discounting how well it should scale with the kaioken*, the benefits of Gero's augmentations are hilariously worth it. Baseline power, strength, speed and durability higher then a novice super saiyan, infinite energy and stamina, the inability to be sensed,
no inhabitation to getting stronger via ki training, slower aging and thus an extended lifespan and only requiring water for sustenance. That's some of the best human augmentation technology in fiction I have ever heard of, it's a straight upgrade.
As for King Kai's Kaioken? They probably figured they wouldn't be around long enough to learn it and master it. Remember, Goku picks up techniques with terrifying speed. He learned the Kamehameha by watching Roshi do it once and he didn't even know how to access his energy!(or Ki as I'll be calling it)
Tien and Chiaotzu were actually there longer then Goku was. Remember it took Goku half a year to travel to snake way meaning he only trained there for around six months, those three plus Piccolo got there much faster then Goku did. At the very least they got there right after Goku went off into space which was what? A month after the battle against Vegeta? 2 months? Something like that. Granted Piccolo got wished back a week later and yamcha 130 days after that(around 4 months) and Tien and Chiaotzu four months later still giving those two a grand total of 8 months with King Kai, two months longer then Goku.
And even then they could still get back to King Kai anytime they wanted! Kami is more then capable of transporting himself himself and others to the check in station in Otherworld and from there it's just a couple days journey to King Kai's place(if that since everyone is now much stronger then Goku was during the Saiyan Saga and consequently much faster). And then after Goku comes back a year later, they could always either use him as a taxi service to King Kai or get Goku to teach them the Instant Transmission and go there themselves. Really they had all the time in the world to train with King Kai, they just never bothered because only Saiyans were allowed their own real agency in dragonball.
It isnt the same as Saiyans, every single race that isn't native to Earth seems to have a transformation. Namekians have two, Arcosians, Saiyans, Makyans...All of them.
In order, tell that to King Kai with his Kaioken technique, tell that to Guru and his potential unlocking power, tell that to Gero and his android technology, tell that to Elder Kai(who specifically called transformations showy, wasteful and a crutch for power) and
his potential unlocking power and tell that to Whis and his training on how to access God Ki for mortals. Transformations are useful and the races that have them are lucky, but they are not inherently necessary. Not all races do, Hit, 17, Toppo and Jiren for instance are four of the most powerful fighters in the Tournament of Power and they
don't have transformations.
There are alternatives to transformations, and by Super the human Z-fighters have almost constant access to all of them if they wanted too. Their lack of doing so is their own failing and the reason they fell behind the saiyans, not their lack of innate transformations.
Krillin did the same thing.
As did Yamcha and Tien actually, though Tien might not count. All the human Z-Fighters are supposed to be freakishly good prodigies for human martial artists, the best of their generation.
*I always figured that 17 and 18 would actually be able to use the kaioken at an even higher level then Goku and for far longer. See here's my reasoning, Goku's durability pretty much stems from his ki, the higher his ki the tougher he is. But it's not perfect, like a circuit that's having far too much energy being channeled through it, there's only so much it can take for so long, channeling
too much power is straining for Goku, either from the various super saiyan transformations(other then Blue) or from using the Kaioken technique which explicitly boosts it's user past their current limitations at the cost of straining their bodies like hell(even more then the Super Saiyan 3 form). But 17 and 18 are different, sure they can use their ki to raise their durability like Goku but thanks to their augmentations their
baseline durability really is tough enough to tank a planetbuster attack even without any ki boosting it higher. They should be able to handle even higher Kaioken levels then Goku simply because they have such ridiculously tougher bodies then him and keep it up a hell of a lot longer thanks to both that innate toughness and their infinite energy reactors that keep them from ever running out of energy and getting tired.
Gero's augmentations plus the Kaioken really is a broken combination, never mind when you add in Elder Kai's Potential Unlock and/or Whis's God Ki training.