While I agree with you that there are nice "just our couple" paths, I would disagree with your opinion that there are also two major NTR routes. I know that 3Diddly himself calls them soft and hard NTR, but the soft NTR paths are actually more the sharing/swinging/NTS paths, since our couple is in this together. Mei is not going behind the players back, on the contrary.
WDR has, after playing them myself, two pure romance paths (with and without rivals for affections) with several subroutes (mostly text variants, but also events), two major sharing/swinging/NTS paths (more dom or subish) with subroutes (here with greater text and event variants depending on your stats and traits). If you want to replay these subroutes, you must set saves because ren´py will replay only 1-2 variants per event. For example I have some route variants for 2/3 of the game which have to be saved. The game does not have them in the gallery at all.
Hard NTR also has several path variants, but these differ mostly on how much and hard you are toast.