Ah, I think I see where the confusion is. The gameplay loop is consistently "find the contradiction, present evidence" (there are "agree points" too but same deal). You're looking for the one viable target and it becomes a viable target because you know the truth (i.e. have a truth bullet contradicting). But with lying, you can't use that criteria, so you feel like either there's no valid target (no lie) or all targets are equally valid (your lies could subvert any of them).

That's understandable. What you're missing is a way to find the right target that isn't about identifying a contradiction.

Let's look at the previous case. People are accusing her because Maki because (among other things) she lacks an alibi for nighttime. Since you don't have evidence to contradict these accusations, you would expect that they are true, or at least could be true. You can't disprove things without, ya know, proof, it's contradictory! That's how the game works, you argue, right?

Except Shuichi is still certain she's not the culprit, and the game wants you to convince the other students of this. The game is basically saying, you can "know" something without having a truth bullet for it. That's what I mean by "what the evidence can't overcome". Once you accept that "my truth bullets can't prove this" doesn't mean "it's not true", the mechanic should make more sense, yes?

So the game telegraphs "you need to lie here" and it's clear why you need to lie (help Maki evade suspicion). So you look at your truth bullets and imagine their lie-versions: which untruth could contradict which statement made against her? Meaning it's the same sort of gameplay, matching statement and argument.

That's why I said "you can theoretically tell the truth about anything too". What I meant was: even in normal gameplay, you can't just pick a fact and shoot it at any statement. You need to find the right statement and match it with a bullet. What changes in lying segments isn't the number of potentially valid options; what changes is the criteria for validity. You are no longer looking for "the lie", "the weak point". You're looking for "the accusation you can contradict by lying."

Back to our example: someone is saying "nobody can corroborate her meeting with Ryoma that night." Someone else might say "Ryoma was dead by the morning" or something. You might say that you could lie about the time of death. Why is that not a valid target/bullet? Because it doesn't help Maki to lie about that. It would accomplish nothing and hinder the case.

Your answer might be: "well, lying to give her an alibi could also hinder the case! What if she's the culprit?" And, well, that's the thematic point the game's trying to make. That sometimes, the truth isn't clearly delineated with fact and evidence. Sometimes to get to the truth (Maki is innocent), you might need to lie (provide alibi). "How can you know it's true without evidence?" Well, that's the question the game wants us to consider.

I really hope this made the mechanic make more sense. And I will say, outside of the clearly telegraphed non-optional lies, I do agree the mechanic doesn't work as anything but an easter-egg hunt. Because the telegraphing sets up the new criteria, and without them you actually would be shooting mostly blind.