> Personally, I think one of the answers to "tech seems to have stalled" is that it's easy to underestimate how important cheap computational power is, even without "AI", to moving forward. For another example, as fantastic as the 1960s space projects may have been, I think they just weren't economically sustainable, so it isn't that amazing that they didn't become a self-sustaining industry right away.
I think it's also possible that technological process happens in fits and starts instead of at a continuous or even a continuously changing rate. Often there's an individual discovery that leads to a spurt of innovation that consists mostly of applying that singular discovery to different problems.
For example:
* The late 19th and early 20th century saw very fast innovation in vaccines and antibiotics, because the discovery of effective vaccines and antibiotics was general enough to solve entire classes of problems all at once. It seems like a lot of innovations all at once when you manage to find extremely effective treatments against polio, smallpox, measles, syphilis, chlamydia, typhus, typhoid, tuberculosis, etc., etc., etc., but really that was just from a couple of extremely general inventions playing themselves out.
* Steam engines led to large-scale mechanization while electrical power led to small-scale mechanization in two relatively fast and concentrated chunks. In both cases, the invention of a general technique for powering machines led to lots and lots and lots of machines.
* Marconi's wireless telegraph was invented in 1896, leading to different varieties of radio, television, and radar.
* Airplanes might be another example. I don't want to dismiss the huge difference between a Wright Flyer and a Boeing 737, but "make the airplane out of aluminum" and "have a tube that the crew and passengers can be inside of" are both pretty obvious improvements once you've figured out large-scale manufacturing and the Bayer process, both of which we had ahead of time. I guess jet engines were another breakthrough, although we kind of had them already and they're basically just rockets except they consume oxidizer from the air instead of carrying their own.
* Rockets. There were less than three decades between the V-2 and the moon because it turns out "building a big rocket" is the hard part. OK, there are a lot of other hard parts to landing on the moon, but they're hard in the way that they're achievable by any sufficiently well-funded and motivated group of people with rockets, but nearly impossible without rockets. As you point out, Falcon 9 is significantly more advanced in certain ways than Saturn V, but the low-hanging fruit was reaped by Werner von Braun.
* Computers: just like the Saturn V is basically a very, very, very large V-2 and so is the Falcon 9, we're basically using very, very, very large (logically large; physically small) versions of the computers we had in the 1970's. The fundamental discoveries in computing are all basically done; the rest is just playing itself out. The reason it seemed to take longer to play itself out is because computers are a self-compounding invention: you can use computers to design computers, and you can use better computers to design better computers. Also, having computers makes a lot of other things easier, so you get a lot of innovation from that, too.
Fusion, promisingly enough, also seems to be one of those technologies that will just unlock a bunch of really, really powerful innovations, seemingly all at once, because of how many problems we could solve by just throwing lots and lots and lots of energy at them. (Some discussion here: https://www.youtube.com/watch?v=8Pmgr6FtYcY . Also, the excellent book "Sustainable Energy - without the hot air" develops rough upper bounds on the amount of sustainable energy that the UK could produce and the amount of energy the UK consumes, ultimately leading to the bar graph Figure 18.1 here: https://www.withouthotair.com/c18/page_103.shtml. Later discussion of nuclear fusion places the same bar graph, to scale, next to the sustainable level of fusion power production on Figure 24.17 here: https://www.withouthotair.com/c24/page_173.shtml.)