I have the original discs (2 CDs in a DVD case republished by "XPLOSIV").
My computer doesn't have an optical drive, hence I bought it on GOG.
I figured it would just be easier and cheaper than buying a SATA optical drive and cutting the front of my case.
Sadly the unofficial patches (resolution etc) don't work on the GOG version.
On top of that, the GOG version doesn't even have the world and script editors.
This is my first game on GOG, so I've no experience with it.

1. Is it possible to get an older version, or perhaps to just DL the ISOs?
2. Is it normal for GOG games to have major components missing?

The newest version of Arcanum that GOG just released does not work with the unofficial patch, high res, high quality, etc. from what I hear.

I'm doing a playthrough right now with the hotfix. Everything works.

I reinstalled and even tried the "verify/repair" option and it still won't work with any patches, and is still missing the editors.
I'm guessing people still have files from an older install, and that the hotfix has removed these things unless you already have them.
The current GOG version doesn't seem particularly usable if you install it from scratch.

I borrowed a laptop with an optical drive and did this:

Install folder taken from an installed version from the XPLOSIV release CDs.
Applied official patch v1074.
Applied UAP 091225 with all options ticked.
Added DDrawCompat v0.2.1 github.
Installed HiRes with the following config.ini:

//Arcanum High Resolution Patch Settings

//Basic:
Width = 1280 // original: 800
Height = 720 // original: 600
DialogFont = 1 // 0 = size 12, 1 = size 14, 2 = size 18
LogbookFont = 1 // 0 = size 12, 1 = size 14
MenuPosition = 1 // 0 = top, 1 = center, 2 = bottom
MainMenuArt = 2 // 0 = black, 1 = fade to black, 2 = wood
Borders = 1 // 1 = add borders to most UI graphics
Language = 0 // 0 = English, 1 = German, 2 = French, 3 = Russian

//Graphics:
Windowed = 0 // 0 = fullscreen mode, 1 = windowed mode
Renderer = 1 // 0 = software, 1 = hardware
DoubleBuffer = 1 // 0 = disabled, 1 = enabled (unless windowed)
DDrawWrapper = 0 // 1 = install DDrawCompat wrapper
ShowFPS = 0 // 0 = no change, 1 = always enabled

//Advanced:
ScrollFPS = 60 // original: 35, max: 255
ScrollDist = 30 // original: 10, infinite: 0
PreloadLimit = 60 // original: 30 tiles, max: 255
BroadcastLimit = 20 // original: 10 tiles, max 255
Logos = 0 // 0 = skip Sierra/Troika logos
Intro = 0 // 0 = skip the main menu intro clip

I'll attach a screenshot comparing both installations.
GOG version on the left, patched CD version on the right.

Just as a general inquiry, have you made sure to install the patches running as admin? Likewise, are you using Galaxy to launch the game or have you tried running it directly without Galaxy?

Like somebody else said, looking at: https://www.gog.com/forum/arcanum_of_steamworks_and_magick_obscura/recent_hotfix_and_the_essential_unofficial_patches it seems the new update may have goof'd something.

Skip this
Added DDrawCompat v0.2.1 github.

do this DDrawWrapper = 1 // 1 = install DDrawCompat wrapper. Save, then run the install.bat. You have to run that everytime you make a change in the ini.

or just go to settings on arcanum through gog and rollback versions.

Nope. Everyone has WorldEd.exe because the UAP includes it, and the UAP + HIghRes 1.5 work just fine, at least with the current backup installer from GOG.

I also have installed the levels hack, and the HQ MP3 music and townmaps. Everything works perfectly in Win10 Pro 1803.

The only (slight) problems I saw were when installing only the UAP over a clean GOG install. All the problems I saw then were "fixed" after installing the HighRes patch (default settings).