People who lived through the time consistently report that PCs had to reach about 300MHz before they became as responsive as a 25MHz Amiga. Part of this is the design of the OS: Amiga gave user-input interrupts the absolute highest priority.

It is not only that. I remember reading some article where someone did actual measurements. Some of the delays are attributed to just how for example keyboards as such work like amount of movement needed before an electrical keypress signal happens and stuff like that, plus the whole processing chain following. And that is where these older computers are much much faster, because USB or worse, Bluetooth, only allow for so much low latency. Plus there are insane amounts of signal processing steps before it even arrives as an interrupt in the CPU, let alone is processed into some actual OS input event, and then it still needs to go through various levels of application software layers. And that is just the input side, the whole thing has to lead to screen updates and this is another level of technocraziness.

Amiga keyboard uses pretty much same architecture as PC PS/2. Microcontroller in the keyboard talking over serial (~10Kbit/s), pushing keys as soon as they are pressed, another microcontroller on motherboard generating interrupts per key. USB is pooled at 125 Hz. While yes, PS/2 and Amiga keyboard will have lower latency, does ~7ms make that big of a difference?

Musicians can feel latencies of 1ms. It makes a difference.

> Amiga gave user-input interrupts the absolute highest priority

That’s a pretty bad idea in general. Handling priorities properly is absolutely essential for the stability of a system. I’m not familiar with Amiga, but systems weren’t known for their stability back then. Whole OS crashes were much much more common back then.

A typical operating system should not have stability issues just because of badly prioritized interrupts. You may have severe performance issues, sure, but if you're crashing because someone didn't handle an interrupt in time, someone designed something wrong. Maybe it's not software's fault and some hard engineer made bad choices, but this is generally not true today since no mass market OS actually guarantees interrupt latency.

Athlon + Windows 2000 was, for me, the first time a PC did not feel outright sluggish relative to the Amiga 500.

Cold booting my 7 MHz A600 to a fully loaded, functional and responsive desktop takes 17 seconds from hard drive (I just measured). Pretty decent, I'd say.

There's plenty about Amiga that is and/or feels instant. My workhorse is a 14 MHz A1200 and I use it at least once a week, so I get plenty of opportunity to compare. For its intended use cases, most things feel very snappy. Then there are of course areas where it doesn't stand a chance compared to a modern PC, even if the workload is "Amiga sized". Decompression and picture downsampling, for example.