As to the rest:
I've never heard anyone claim that the computers of today don't "feel" any faster than computers of 20 years ago,
Interesting, I find it to be a fairly common refrain. In fact, what I'm saying is basically just a paraphrase of Wirth's Law:
but if you feel that way I just don't think you're living in the same universe as those of us who walk around with quad core computers in our pockets.
Well, I walk around with a quad core computer in my pocket as well, and I still stand by that assertion.
Please define "other stuff" and where you draw the line between that and simply "browsing"
I'll allow that there's some subjectivity there, but when you're talking about a "web application" like, say, Microsoft Outlook online or something, or a programming editor or a CAD program or an image editing program, I can't help but wonder if that stuff should really be done purely "in browser" as opposed to being handed off to another program.
OTOH, I understand (some of) the arguments for doing it this way. Having a uniform experience for all clients, the security holes associated with plugins, avoiding the need to deploy software to individual machines, etc. I'd just like to suggest that people spend some time considering if there are other ways to achieve the same end(s) other than continuing to bloat the web browser until it replicates all the functionality offered by the underlying OS.
I don't object to the idea that some software trends towards sluggishness because of feature creep or lazy developers, but I take issue with the statement that computers of today don't feel any faster than computers of 20 years ago because there is a large cross section of computing tasks that are wrapped up in the notion of what constitutes a "fast" computer.
For example, in 1995, running Paintshop Pro and netscape on the same machine was about the limit of what my computer could handle at once. Today, I can run photoshop, chrome, Visual Studio and 2 VMs simultaneously without skipping a beat. In 1995 just trying to minimize netscape could result in a 30 second wait while the system attempted to redraw the windows beneath it.
I have distinct memories of how my brain was conditioned to avoid certain actions because it would render the machine practically inoperable if care wasn't taken to ensure that no more than a few programs or operations were performed simultaneously. Today, even on Windows, I can leave dozens of programs (including the browser with a dozen tabs of it's own) open for months at a time and experience zero slow down; compare this with 1995 where restarting a sluggish Windows PC was a daily ritual because it would just become unusable if left with multiple applications running over night. Even in 1999, if I decided I wanted to play the original starcraft, I needed to ensure that I closed all other applications if I wanted to avoid game-breaking slowdown, and even with that, accidentally hitting alt-tab resulted in a 30 second wait while the desktop rendered itself and another 15 seconds for the system to return context to the game. Today, I can leave all my work open in the background, play a few games or seamlessly alt tab to adjust my playlist and then continue working afterwards without any impediment. in 1995 it took my computer 20 to 60 seconds to boot, today, thanks to the SSD, it takes 8 seconds maximum from boot to desktop on Windows, and even faster on Linux.
Today, you don't even have to think about performance (as a user) because the vast majority of common computing tasks can be performed effortlessly by modern systems.
An experience that is uniformly slow and uniformly broken a different way on every browser...
And it is a somewhat legitimate argument. Whether or not it justifies having the browser subsume everything is, IMO, an open question.
This would be TREMENDOUSLY better than trying to make the browser into an OS.