Look at new levels made for old games, with high levels of detail in the architecture, but still very readable:
Eh, those aren't really that detailed... e.g. the entire Tomb Raider scene you show has less polygons than the tail in that bat thing in the "new games" scene. They might be more detailed than the base game, but not really as highly detailed as what you'd see in a AAA game, even from the late 2000s.
TBH i do not think it is so much detail or post processing that is the problem, but contrast (if anything, post processing effects like SSAO can add depth to an otherwise flat scene and make shapes and volumes more readable - though i guess you had bloom effects in mind which often do wash out things if they're not set up properly to match the area's lighting).
I was playing Dishonored 2 just now and had the same issue - the game tries to alleviate that by adding white outlines in everything you can interact with, but it can still be hard to read a scene, especially when the game decides it is a nice idea to randomly making everything shiny and "bloomy".
It isn't a new thing for me either, i had the same issue since the first time i tried to play Unreal Tournament 3 - there was too much detail everywhere and i just couldn't focus on anything so i had a hard time reading the scene. Initially i thought it was due to the detail and the clutter in the scene but after playing other games that had more detail, i think it is because UT3 had awful contrast - everything was either uniformly shiny or uniformly muted with barely any contrast.
As a sidenote, i do not think turning off shadows would help - shadows give hints for the position, size and volume of objects, so having them enabled, even at the lowest resolution, should make the scene more readable. In terms of post processing you most likely want to disable bloom and sharpening (unless the latter is applied per-object, but i haven't seen many games do that). You most likely also want some form of SSAO (preferably something like HDAO or HBAO since those take surface direction into account instead of just distance from the camera and thus are a bit more accurate), especially if the scene has large geometric clutter as it helps to add some depth to it instead of having everything mesh together (but the quality of SSAO varies a lot from engine to engine... some games, especially older Unreal Engine based games, have horrible SSAO implementations).