Considering that the NeXTStep OS ran on a 1120 × 832, 12 bit, display in 1990 with 12 MB of memory, I'd say more then a year. Judging by modern app memory usage.

Recently watching a Gamer's Nexus video where they tested a new built Voodoo 6 5000, I was impressed watching them install some ancient edition of Windows in which to do the testing, and how snappy and responsive the interface was.

My first computer was a 95 Packard Bell. I was 12 years old at the time, so I might be misremembering, but I swear the interface responsiveness felt immediate.

Dan Luu did various tests on keyboard and terminal latency. Its not pretty. However a modern desktop have a compositor (since Vista, Linux since XFree86 -> X.org, and macOS since forever). This is essentially double screen rendering.

We might need to block all software features for the next decade so we can figure out what's going on.

The C memory model underlying all modern processors does not scale. Most of the time your cpu is sitting idle.

My favourite comparison is that the A16 chip can do 1 million times more operations per second compared to the top of the line System 360 mainframe.

That is to say, a theoretically ideal OS running on the A16 could run every mainframe program in existence until the late 1970s, simultaneously.