(Updated to 115.3-beta (WebKit 614.1.12))
So I've found a workaround that Develop > Disable Images actually loaded Discord and re-enabling Images while the page is displayed, clicking on the folders on the left panel restored the images and switching servers restored images - except for my profile pic on the bottom left corner, which remains blank. But now I can use Discord properly! yay!
Disabling Web Fonts crashed the web page.
Still broken on Version 0.99.116-beta (WebKit 614.1.20) otherwise.