Both Macs and PCs of the time had a very limited ability to run multiple programs at once - Macs had Desktop Accessories (Calculator and Alarm clock, others later), and PCs had TSR programs that would you could invoke in various ways (Borland's Sidekick PIM being one example).
Later the ability to run multiple programs at once became possible - the Mac got Switcher in 1985, then Multifinder in 1987, and there were various methods on the PC for running multiple programs at once.
Even though these were not preemptive multitasking, these solutions were viewed as "good enough" at the time, so there wasn't really that big of a gap with the Amiga.
Also, popularity - it was the early 90's before I saw an Amiga hands-on as a primarily Mac user - the reaction then was more "why would you want this low resolution thing" when SVGA and higher resolutions were somewhat common on both Macs and PCs.
For the PC, there was TopView, MS-DOS 4.00 (multitasking), DESQView and others. However, most people just adopted workflows that weren't reliant on multitasking (not unlike how most people currently use their phones).
Mostly no. People didn't have access to the Internet so most of their computer knowledge came from books or magazines but those tended to be siloed by platform. Even a "power user" who subscribed to PC World or MacUser wouldn't know much about Amiga or Unix.
Byte was probably the most cross-platform magazine at time, and even then there were only so many pages to cover things - it ended up being mostly PC, Mac, and Unix workstations, IIRC.
I can only think of 1 family that had an Amiga in 1985. The only place I could touch a Mac was at a computer store. Commodore 64's were around but, most people had Apple ][ or PC. No internet, just BBS access, maybe CompuServe.
In terms of this actual PC user in the 80s (though not as early as 1985) I simply didn't know about what the Amiga was capable of. I knew no-one with one, it wasn't really mentioned in the PC magazines other than in passing, and I couldn't afford one (since I had a PC). It was a lot harder to know stuff about other technology back then unless you had connections or were going to events, so most users were in whatever bubble they were in.
People didn’t react to things in the 20th century in the sense in which “react” is used today.
I mean maybe a few people wrote letters for the letters columns of some magazines. It’s logically possible some of those letters were published some weeks later…magazines had lead times…and then a few issues later a response letter was published. But probably not.
OK, Usenet was also possible but in the 1980’s that was a few thousand people who could react in a way close to how we talk about reacting today. Otherwise ordinary arguing with people in meatspace was about the limit. You would have had to find other people with strong opinions.
It’s worth noting that in 1985, the C64, Vic20, ZX Spectrum, 8 bit Ataris, and Apple II were the ordinary home computers, not PC’s and Macs. On top of that the Amiga 1000 had limited distribution relative to PC’s and Macs (which in turn had limited distribution relative to C64’s etc.).
Later the ability to run multiple programs at once became possible - the Mac got Switcher in 1985, then Multifinder in 1987, and there were various methods on the PC for running multiple programs at once.
Even though these were not preemptive multitasking, these solutions were viewed as "good enough" at the time, so there wasn't really that big of a gap with the Amiga.
Also, popularity - it was the early 90's before I saw an Amiga hands-on as a primarily Mac user - the reaction then was more "why would you want this low resolution thing" when SVGA and higher resolutions were somewhat common on both Macs and PCs.