Again, no-one is saying it's complicated.
Clearly, the guy's NOT like you. Like I said, not everyone consumes game content the same way.
No, he isn't. He's saying the game does not contan an efficent way to check certain information. That's a VERY different thing. If you want to disagree with the dude, then disagree with what he's actually saying.
No-one is saying to "change the game". The guy is saying to "improve the UI". Those are two VERY different things.
No, it doesn't. It tells you how many exhibitionism points you've earned. That's not the same thing. In order to see what scenes you've unlocked, you need to talk to each girl individually then go to their exhibitionism scene hub (cafe or beach), which is nowhere near as quick or efficient a process as the option that Lain's mod included.
Why should they remember? They might have last played the game three months ago; why would you expect them to remember everything they did and did not do in a game they play irregularly?
Again, the fact that you've played through nearly 900 days, and others have played through 23 times, are not the only ways to play the game.
You don't need to get it. The guy (and others like him) are telling you that they found the mod helpful, as an efficient hub for seeing certain information at-a-glance. The fact that you personally don't care about having that information so readily available is irrelevant; they do care, and they're telling you they care.
What he is saying is very clearly "I like access to information in an efficient way", and the response he's been getting is "but you can see the information just as easily by spending twenty five minutes clicking through eight different conversations, so why do you want a faster way to see that information?"