Certainly one can get a PGMP-12 on a tech 5 world...
Sure, you can import whatever you can afford.
Remember what TL means- it means what the prevalent tech is on the planet.
You don't understand. Let me try to get the point across again
You're conflating technical capabilities with technical knowledge, something people in our post-industrial culture often do. The two are only casually linked.
I can build a crystal radio set with TL
0 technical
capabilities after the TL
4 technical
knowledge is developed, I can make gunpowder with TL 0 capabilities after the TL 2 knowledge is developed, and I can make a pot-in-pot refrigerator like the ones used to keep vaccines safely cool in Nigerian clinics with TL 0 capabilities once the TL 4 knowledge is developed. Knowledge is more than half the battle. Often times the capabilities existed well before the knowledge caught up.
In a caveat emptor free trade environment...
... TL 0 people are going to know about radios. They're not stupid and they're trading with people who use them all the time. Sooner or later, someone is going to trade them the knowledge of building crystal sets and building their own crystal sets is going to be far cheaper than trying to trade for a TL 7 transistor radio they cannot repair.
... that is going to mean what people can afford, and the expertise the planet builds up being able to support it.
This isn't about planetary development or technological uplift. This about people using lower TL capabilities to build certain items thanks to the preexisting knowledge from higher TLs.
Of COURSE everyone would like to live the TL15 high life. But clearly it doesn't happen, and I'd say it's because of the economic underpinning of the planet, not enough value produced to trade and not enough native industrial capacity, and the skills for maintenance much less manufacture at TL15 are not viable because there isn't enough 'installed customer base' for it. Because they can't afford it.
No. Fred and Barney aren't going to try and build Bedrock's first arcology in some attempt to bootstrap their world to TL F.
Instead, they're going to have gunpowder because there's no reason you can't make it at TL 0
once the idea is known. They're going to use pot-in-pot refrigerators, they're going to make and store hay, they're going to wash their hands after they defecate, they're going link their towns by semaphores, they're going to operate animal drawn railways, and they're going to be making, building, and operating hundreds of other things with their TL 0 capabilities because all the knowledge up TL 1 through F has already been developed.
Fred and Barney don't need to reinvent the wheel so they're free to build the best wheel they can with their capabilities. They don't need to reinvent anything. All they need to do is attempt to recreate higher TL ideas with their lower TL capabilities.
How can you have a B-5 starport?
That question has been answered for decades now.
Well I suppose the same way you can have a high tech factory making electronics in some third world country that is profitable to do because of the lower labor costs while crops are grown via oxen and everyone gets around by scooter at best, or the US Ulithi base in WWII while the natives are TL2-3.
And that's the decades-old answer.