Thanks for this. Not being an expert on the topic, it was hard for me to be sure if Tora's overly aggressive compression of images or Mortze's own admission of using lower level resolutions and short render times was the cause of the poor quality images in their games. They have said that we can't see the difference between the original and compressed images but your sample images clearly show the artifacts that I see in all their games.
The first Christine was rendered by Phreaky, so hopefully Mortze has nothing to do with what happened here since all the rendering for this project was done in 2011 and all they did was compress it (which is sad, the old size was not bad at all, it's actually on the small side for a lot of stuff today.)
As far as for other more recent Tora games, that's something else. I hadn't heard about them doing this (I dropped their Patreon because Tlaero kept filling my inbox whining about how awful piracy was. Oh, irony). But yeah, Shorter render times will result in less complexity and math on a scene calculating exactly just how light affects the scene, reflecting off objects, partially penetrating stuff like skin and fabric, etc. Basically, less detail. Lower resolutions hide that lack of detail (A small 1080p screen like your phone looks amazing, while a 65"+ 1080p TV, you can start seeing the flaws the closer you get to it.
As far as compression goes, most times you can't really tell unless they released a higher resolution version of something for comparison, like we have here. Going back to the TV example, It's like how 1080p was great until you saw a 4k TV at the same size. Meanwhile, additional render time is like how you thought 4k was great until you saw HDR.