Comparing to Win 3.11 or 95 is irrelevant. We were talking about workstations. The Mac didn't have a workstation level OS, while Irix and NT did. Unfortunately the way people remember the classic OS and what it actually was like to use day to day are world's apart. Sure you could be productive with it, slowly and with a lot of hair pulling moments.
Most people who try to remember their computing and gaming experiences from 20 years ago or more tend to whitewash the crashes, the bugs and the downsides and instead mentally upgrade those experiences to something that more closely resembles modern computing. Instead of remembering the bomb sign that appeared on the screen every two days, they only remember it happening a few times ever. When they actually come face to face those old machines and software they realise their memories aren't reliable. It really was crap back then. In fact, it's impossible for anyone to remember a computing experience accurately. If you, I or anyone says they can they've fooled themselves. In the words of Richard Feynman 'The first rule is not to fool yourself, because you are the easiest person to fool!'
In my office at work at this very moment, I have two computers running Mac OS 9.2.2(B&W G3, along with a beige G3 upgraded to a G4). I also a computer running Irix 6.5(SGI Octane, along with a dead O2 that I'm trying to get working) and at any given time multiple computers running OS X-generally a Quad G5, a Mac Pro 1,1, and my MBP, but also sometimes other systems(both G3s can also boot into X).
I occasionally use the G3s for some proprietary applications I have that require the "classic" Mac OS in a real(not virtualized) environment and need a physical ADB port since they rely on HASPs for piracy prevention. I own the Macs, and also occasionally fart around on them-whether it's writing up a document in WP 3.5e and using Chemdraw 7(I'm a chemist) or taking a break for a few minutes to play Civ II
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I never really use the Octane but "babysit" it and can troubleshoot it when something goes wrong. I don't own it(University property) but occasionally other folks drop by to use Felix(NMR offline data processing) and some protein modeling software on it.
The OS X Macs are, of course, my main machines. I do most of my "work stuff" on the MP and use MBP more for personal stuff, but those aren't 100% defined roles(I own both systems personally). I use the Quad for some legacy software that is PPC only, and before I hauled the MP in it was my main work desktop. I still use it a fair bit just because I'm "comfortable" on it.
Despite nearing 20 years old(1998 ship date) Irix on the Octane is absolutely rock stable. The last time I turned it off was when I moved offices a month ago.
All the OS X systems are rock stable also. The MP was giving me occasional KPs that I tracked down to a dusty memory slot, but I don't think I've even turned it off since fixing that. BTW, it's somewhat "hacked" as it's running 10.9 despite not officially supporting anything newer than 10.7(an EFI-compatible flashed video card from MacVidCards plus Tiamo's 32bit EFI patch got me to 10.9).
As much as I love OS 9, comparing it to the contemporary Irix or to OS X-whether on PPC or Intel hardware-really does make realize a lot of the limitations of things like cooperative multi-tasking and not having protected memory. Yes, I can certainly multi-task in OS 9, but-as you said-until you compare it side by side with modern hardware you don't appreciate how bad it is. For running a single application, OS 9 is often perceived as being faster and more responsive than OS X on the same hardware. That is true, but if you're running something processor intensive in the background, you might as well forget getting anything else done. Heck, even copying a big file from a flash drive to the hard disk can grind the system to a halt until the copying operation is done. Most of us don't even think twice about doing something like this in OS X. Despite the fact that I can actually(lightly) browse the internet somewhat pleasantly if not doing anything else in OS 9 thanks to Classilla, I wouldn't dare do it if-for example-running a big calculation in Spartan both because Classilla will be so slow as to be unuseable and a bad script on a web page could cause a complete crash that would make me lose everything I'd done up to that point.
I should also mention that the B&W G3 is more or less stock other than an upgraded hard drive and more memory while the beige is heavily upgraded. It has a Sonnet 1ghz G4, 15K SCSI HDDs run off a factory UW SCSI card, a Radeon 7000, and a couple of other odds and ends added. It's much faster than the B&W, but also less stable under OS 9. In fact, it's so much so that I'm considering transitioning it back over to full time OS X use(it actually runs Tiger really well).
One last thing-there are a lot of good parallels to be drawn between OS 9 and the much hated Windows ME. Both came out around the same time, and represented the last evolution of their respective OS "type"-ME was the last version of Windows that was basically a GUI wrapper around DOS, while OS 9 was the last of the "classic" Mac OS. OS 9 seems to be remembered very fondly now, but on at least a couple of systems I've actually regressed to OS 8.6. It offers most of the same features and software support, but I've found it somewhat more stable on a lot of hardware than 9.2.2. Of course, on a lot of hardware, OS 9 or later is the only option(and in some cases you even need a version of OS 9 specific to particular hardware).
