And no, software efficiency isn't even the main factor. Not even close.
Just a few pointers: polling on peripherals instead of interrupts (i.e. USB vs. PS/2 and DIN) introducing input lag, software no longer running in ring-0 while being the sole process that owns all the hardware, concurrent processes and context switches, portability (and the required layers of abstraction and indirection), etc.
It's a bit cheap to blame developers while at the same time taking for granted that you can even do what you can do with modern hard- and software.
Everything comes at a price and even MenuetOS [1] will have worse input lag and be less responsive than an Apple II, simply because you'll likely have USB keyboard and mouse and an LCD monitor connected to it.
Big projects would pretty much kill it and the occasional crash was to be expected.
Sure, firing up VS6 on more modern hardware let it fly by comparison, but then again its features paled in comparison to those available with modern VS.
On the other hand, I don't use VS anymore, since VSCode is all I need and runs faster than VS6 back then (even on my 5 year old mid-range laptop) so no complains there.
You could load and start an entire game on that thing (albeit from a ROM cartridge) in less time than a 2000-era PC took to just POST :D
So PCs were a regression in performance in that regard compared to 1980s home computers and micros.
Compared to my recent company laptop which needs at least 2 min. Even more before I can work productively. For Windows 10.
It's definitely not dependent on hardware. Even not on functionality (I do the same on both machines).
It takes things way beyond simply "emulating Javascript in Javascript", yet is presented so well that you barely notice the transition from current (2014) reality to a comically absurd future.
So like 2009 compared to 2021? Based on that, I'd say even more inefficient webshit.