Yo, Gravis, feel free to mute this cause it's just some details around how wrong and dumb these people are (also with the caveat that anything pre-1997 was historical to me too) but:
- SLS, the first "major" commercial Linux distribution, was first released in 1992. By 1993 it had already spawned several descendants, including Slackware, which is still being developed and maintained. You want a bootable Linux distro in 1993? You could buy Slackware off the shelf at Radio Shack! If you went to the library you could download the floppy images from Walnut Creek or a number of other mirrors! GNU GRUB per se was first released in 1995 (prior to that LILO was the bootloader of choice, otherwise people used loadlin which just booted Linux from DOS) but LILO was/is a general-purpose bootloader and could effectively boot basically all x86 OSes and could be used independently of Linux with a bit more pain than modern GRUB.
- Again by 1993, Linux ran X and could run all DOS software via dosemu (released in 1992, was pretty stable by 1993, certainly no worse than running DOS on metal) and had ports of already vast amounts of Unix software, commercial and otherwise. With X11 running and Motif building (albeit still under commercial license at the time) it was fully capable of running basically any desktop Unix software or X/Open or POSIX-compliant whatever you felt like compiling for it; by 1994 it had iBCS2 compatibility and so could run basically all commercial Unix software compiled for x86.
- Installing Linux from a mainstream distro in 1999 was uh, pretty easy? SuSE had a high-quality graphical installer that was derived from YaST even! Making Windows and Linux coexist actually got harder into the 2000s and then especially in the early UEFI days because MS started doing things like highjacking the boot order when you updated Windows service packs.
- The GRUB manual was not only available in 1999 it was usually installed locally if you were using GRUB instead of LILO, and has been online at gnu.org (currently https://www.gnu.org/software/grub/manual/grub/grub.html) since 1995; whatever else you can say about the GNU project, they've always prioritized high quality documentation.
- I don't know what "eating itself by way of ever-changing drivers" is even supposed to mean. That's Windows or Netware, dude.