I feel like the 3 setups make sense as a "continuation" of sorts.
In 1:5 world shit started hitting the proverbial fan. Dudes get princess treatment cause they basically can pick and choose as much as they want. Girls get desperate a bit too, so that even the "uglier" dudes can "pull something".
In this 1:20 world, the ratio is already tragic enough that stuff changed. Men are in actual danger. Special "groups" got created - men guardians - to protect men.
The 1:39 just pushes the envelope even further. There are full blown schools that train men guardians, there is so little dudes that having 1 in a whole typically 20-30 people class is not guaranteed. Men are forced by law IIRC to go and donate sperm for artificial inseminations and stuff, cause its more humane than forcing dudes to fuck 40 girls.
The biggest difference is just how stupid the dudes are. 1:5 dude was already a retard, a "nice guy" who lost a girl cause he wasn't fucking able to treat her like a special being - he was the same with every single other girl. His behaviour didn't change one bit after isekaing and is borderline dangerous in the new world.
Dude in this 1:20 one is literally brain dead. He isekaied to it as a kid, he spent 15 years in it, and yet he behaves like he got transferred yesterday or even today at morning or something. Hard to say how much of his stupidity of not recognising girls comes from artist way of drawing, and how much from MC being actually mentally handicapped.
Dude in 1:39 seems to have a brain and depending if we add the R18 side of things to the calculation - it seems he freaking knows what he is doing.