Presumably, if Goku has gotten strong enough to require nukes, he's had a few battles and zenkais because of it. So he could feasibly be way stronger than 20 at that point. And that's assuming they don't underestimate Goku and he didn't end up decapitating the world government before they could bring them into play.
Well, again, the point is that the saiyans as a whole didn't
really care if Goku lived or died, or they wouldn't have sent him off to Earth that way anyhow. They may not have even known what the strongest power levels on Earth were.
My understanding though was that while we do have synthetic rubber, it's still inferior to natural rubber, and you need natural rubber for things that need really high quality hard wearing stuff. Like aircraft, and laboratories. Hence natural rubber is hugely important to our society as well.
It's important, but it's not on the same level as oil.
You're overestimating the Garenhulders. While they can do small improvements and adapt principles to reality, they don't make leaps from, "these two substances are a bit alike," to, "oil to rubber." They have not even had the concept of synthetic rubber. They extract everything. If you suggested synthetic rubber to your average person — your average chemist, even — they'd blink and ask if Semdal had burned down at some point. Then they'd call you nuts because alchemy was discredited a century ago, didn't you hear the news?
Eheh... Alchemy. Discredited. yes.
Um... they
do know how chemistry works, right? They don't just have these random recipes that somehow work by magic and no one knows why? Because that would make it basically impossible for them to, say, design rocket motors for ballistic missiles, or construct new oil refineries.
And just to be clear, Garenhuld has
plastics, right? Like, PVC, polystyrene, polyesters, polyurethanes, and so on?
See, natural rubber is basically polyisoprene, it is
just another polymer. Do the Garenhulders not know this and just think of rubber as this magical substance that needs no analysis or comprehension? If so, it's kind of surprising that they ever learned to vulcanize rubber in the first place, without which it's pretty well useless for most of the things rubber is useful
for.
As far as I can tell, the possible explanations for "no synthetic rubber on Garenhuld, it's just not a thing they would think of" are:
1) Garenhulders have scientific chemistry
at all, in which case they shouldn't be able to design oil refineries or rocket engines.
2) Garenhulders are so incurious that even with an understanding of scientific chemistry, they don't even bother to learn the chemical makeup of well-known substances. In which case they probably wouldn't have developed scientific chemistry in the first place, and even if they did their material science would be extremly poor, which again would interfere with their ability to build rocket engines.
3) Garenhulders have scientific chemistry and know the chemical formula for ubber, but are utterly lacking in plastics. This raises many of the same problems because plastics are used for a lot of things and are one of the main reasons oil is so important anyway...
4) Garenhulders have scientific chemistry, know the chemical formula for rubber, and have successfully made a variety of plastics... But are inflexible that they are incapable of the leap "well, we've polymerized several dozen OTHER chemicals, why not polymerize this one too?"
...
My problem is, I'm losing my ability to comprehend how Garenhulder technology works, especially in the context of going medieval to Information Age in 300 years.
Except in the context of, say, large numbers of Garenhulder decision-makers being meat-puppeted by some mind control entity that causes them to make character-breaking innovative decisions. Just having saiyans introduce the relevant technologies so everyone else can see how beneficial and profitable they are wouldn't be enough, because the Garenhulders as described would be functionally incapable of engineering. In the same sense that a person cognitively incapable of understanding the concept of "turning" would be unable to drive a car.
I don't mean to be rude by saying this, I really don't. I just think that you may have played up the Garenhulders' anti-innovation to a point where it conflicts with their ability to maintain a technological civilization.
Why don't they take the step anyway? For greater independence, if nothing else? Somebody must have thought of it at some point. Because Garenhulders have a flinch response to new ideas, even within the same field. Apply engineering principles to this plot rather than that one? Not new; same principle. Figure out how to turn oil into rubber? Old materials, but new concept. One is refining and respecting the old. The other...to them, that feels dangerous.
To a chemist, figuring out how to turn oil into rubber isn't going to feel different from figuring out how to turn oil into any other plastic. And
that process isn't going to feel different from, say, learning that you can extract rare earth elements and make high-capacity electrical batteries out of them. Or that you can make paper out of wood pulp, given that paper is utterly unlike wood.
See, if you told me "Garenhulders have a flinch response to new ideas, but are comfortable with applications of old ideas," I would predict that they would have, say, all the plastics or
no plastics, great aircraft or
no aircraft, and so on. Because once someone introduces the idea of the airplane, they keep poking and refining it, but they'd never have invented it. They might have, say, very sophisticated turboprop planes but not a single hot-air balloon, depending on who suggested what. Then someone proves that jet engines work and they start refining
those, until they have hypersonic ramjet fighters or whatever... but haven't picked up comparatively easy, low-hanging fruit projects like weather satellites because orbital rocketry is "new."
The thing is, we've already established that they have an industrial civilization, which kind of places some constraints on which ideas they already have in their mental lexicon.
If somebody needed it badly enough — "the entire world is blockading us and we have run down every solution all the way down to declaring war, a war we are most certainly now losing" — then they'd risk it. But not before.
This does make Semdal incredibly powerful economically; thus why I mentioned that. It's also why Aramaia sees such advantage in making them a protectorate.
Also I made Garenhuld via random generation and Semdal came up as both tiny and sitting on vast wealth when I did.
See, I am
completely fine with this. My point isn't that Semdal shouldn't be tiny, spectacularly wealthy, and sitting on precious natural resources.
My point is that a natural rubber monopoly in a world where chemical engineers know how to make plastics and routinely produce them
en masse just isn't that valuable... While the oil monopoly you
also gave Semdal is ample to explain their geopolitical power, without even bothering to reference the problematic rubber monopoly.