Although Smalltalk was early computer language from the 1970s, it could not run efficiently on most computers until the 32bit CPUs came along in the 1990s. By then the simple C language and it's OOP hybrids dominated the coding world.
Smalltalk came on the scene before computer operating systems were well developed as we know them now. Hence Smalltalk did a little bit of everything- code, GUI, OS, IDE. This an advantage in providing an unified API to all these services. However all these services are not as well developed inside Smalltalk as in the layered systems we have now.
The Apple Macintosh was released in 1984, Smalltalk ran on it fairly soon after this. The problem was that it wasn't available to the general public, only to universities.
Ok. My memory of it was from a bit earlier, I first saw it sometime in 1986. You would have had to add the cost of APDA membership to the $150 stated in your link. I found an OOPSLA conference report that described seeing a demo of the Apple Smalltalk+MacApp product.
I also found a flyer for Smalltalk-80 on the IBM AT for $1000 from around the same date.
Smalltalk/V (not 286) was perfectly usable on a PC of the day, I ran it on an Olivetti M24 with a paper white display.
The Smalltalk-80 flyer states that an 8MHz 286 was faster than a Xerox Dolphin and 20% of the speed of a Xerox Dorado. The painful part would have been the display, they were just using EGA (640x350) so you couldn't see much at one time. I saw a demo of this and don't remember thinking that it was too slow.
Smalltalk came on the scene before computer operating systems were well developed as we know them now. Hence Smalltalk did a little bit of everything- code, GUI, OS, IDE. This an advantage in providing an unified API to all these services. However all these services are not as well developed inside Smalltalk as in the layered systems we have now.