I keep an old Thinkpad around running Windows XP. Its some 512MHz CPU, so not really that fast. But: It boots faster, the UI feels less sluggish, you can tell apart buttons from inert text, and launching Age of Empires I and restarting my savegame takes like 5 seconds.
I keep this Laptop as living proof that computers did indeed get shittier.
I'm on a thinkpad x230t from over a decade ago, running Linux. It is a bit less vintage than yours, but I can confirm that for the princely sum of £200 on ebay, I can run a window manager and pretty much any software I want.
It replaced a £1500 starbook, which stopped powering on about a month after the warranty expired.
Not quite the same point as you, but I'll agree on something: old hardware that lasts is miraculous.
I remember when windows xp came out. It felt so slow on my celeron 300 mhz (overclocked though) with a geforce 256, sluggish to a point that I happily switched to gentoo.
Of course your Thinkpad most likely came late in the windows xp lifecycle so it feels snappier but the user experience when windows xp came out was anything but fast.
To be fair. Celerons were really terrible. I ran them for a long time (even was running dual celerons on a board at one point) and overclocked the crap out them. Then I switched to an actual Pentium 3 chip and it blew them away. Never went back.
A lot of things definitely got way faster though, they just are things that neither switched to most inefficient (computing wise) ways of doing it (Electron GUI) nor pay the "high resolution" tax.
My first own computer could hold the entire final displayed framebuffer in less than 1MB. The display I use right now requires a bit over 32.5 MB to do so, and switch towards more and more hires raster bitmap as method of drawing interfaces means it's schlepping probably over half a gigabyte every frame.
But things that don't need that? Even for python development (not running jobs, interactive development) my recent switch from Kaby Lake i5 to Zen4 resulted in noticeable speedup. Despite the previous machine already having NVMe SSDs etc.
The web being slow is an example of UI in general becoming slow.
My experience over the years has been that UI frameworks are very fun to write but we'd all be better off if our managers said "no" to them — vanilla HTML is very fast, as is UIKit.
Likewise for development, while Interface Builder gets flack for the file format making it hard to collaborate or even to code review, actually using it to implement a UI from the design team is fast and easy compared both to UIKit in code and to SwiftUI (and SwiftUI is better than some of the other programmatic UI frameworks I've seen, though it also loses points for a WYSIWYG editor that gives up if you look at the keyboard wrong).
The web is slow because it's used in ways that it's not exactly designed for.
This means that even when you try your best, you can end up with very complex code paths for doing things that would be handled through simpler ways in "proper" GUI framework.
It's not really a dig at browser engines - they are very optimized. But they are very optimized because otherwise it would be even more unbearably slow.
I'm not complaining about the browsers themselves either.
IIRC, almost every UI widget in iOS and Mac OS (even way back to 68k) and VisualBasic and Java is a rectangular interaction region, even if the appearance is circular.
A <div> with a background image and an on-click, on-mouse-move etc. handlers, can replicate the look and behaviour with much lower complexity than even the React tutorials I've done (I assume that React is even more complex in production?)
Last tech conference I went to, there was a talk on how to boost website performance by loading your JS in a particular order — at that point, I think you're better off with a website being an img and <img> and <map> and everything more than that being done on the server. Not that this is a good idea, just less bad than having so much JS you need to re-order it to keep load times down.
jQuery seems nice, from what little of it I've seen in practice.
I keep this Laptop as living proof that computers did indeed get shittier.