Here's a fun question: how much of what Starship is doing would have been impossible in the 70s?
In my view, the reason we don't have space colonies already is because we decided not to. Nothing we're doing now was strictly impossible then, just a little bit harder. No one was trying, was the problem.
It reminds me a bit of Brian May. In the early 70s he was getting a PhD in astrophysics, studying interplanetary dust. He stopped because his band, Queen, was doing pretty well. In 2006, he realized no one else had ever picked up his particular avenue of research. He resumed his PhD research and completed it.
Probably a lot. The Raptor engine uses 3D printing, which I don't think was a thing in the 70s.
Modern CNC machining wasn't a thing either.
Nor modern design and simulation software.
Or computers.
I mean, maybe if you really wanted to and money was no object, something Starship-like would be doable, but it'd be more expensive, harder to design, harder to build, carry less weight and likely uneconomical. But the very point of Starship is saving money.
Compared to Starship, sure. But compared to the Shuttle? That's a pretty low bar that's pretty easy to beat.
Starship is basically the Shuttle done right. major differences: Methalox instead of hydrolox & solids. Stainless steel. Uniform tiles. Vertical landing. No cross-range capability.
Any or all of those changes would have made the shuttle better.
Full-flow staged combustion might be impossible without modern metallurgy. The Soviets had that in the 70s but the Americans didn't. OTOH the Americans had the F1 in the 60s and a new version of that would certainly provide suitable thrust to weight ratios. Kerosene means more frequent refurbishment, but still better than the Shuttle.
Vertical landing would be tough with 70s computing but certainly would be possible with 80s computing.