> Cessna 172s flying into international airports have to fly their landing approach way faster than usual for that type of plane because _everybody_ flies approaches at 747 speeds.
This isn't even close to true. https://en.wikipedia.org/wiki/Aircraft_approach_category.
Cessnas approach at less than half the speed of 747s. The safe maximum cruising speed is 20-30 kts short of a 747 approach speed. You would have to be willing to risk your airplane and your life to get a Cessna up to the approach speed of a 747.
My experience landing Cessnas and other light aircraft at airfields where they land the big boys (including busy international ones) is that you approach and land at the speeds that the aircraft you are flying is designed for (which, btw, ATC and the FAA don’t give two shits if you are an international airport, the rules are the same everywhere in the US. I am licensed and have flown in other countries, and it varies ever so slightly, but not in the direction you are implying). I have had controllers ask me to keep speed up for spacing, but they aren't expecting miracles, they know that you simply can't get a Cessna to go above a certain speed.
The rest of your comment also has some dubious claims. I suspect that the top speed was set just below mach 1, not because Boeing had no engineering knowledge about supersonic flight, but because fuel efficiency, and a host of other factors that make supersonic flight difficult. As a counter to that assertion I would point out that Boeing had a supersonic engineering team that started in 1952. They even designed a supersonic airliner that was never built in the 1960s. Hard to believe that they chose not to make the 747 supersonic because they lacked the experience to design an SST while they simultaneously had an SST design and supersonic research team before the 747 was conceived.
The 747 was a groundbreaking airplane, but it wasn't all of the things being claimed here.