In a word: Bullshit.
But I must commend you for taking up the gauntlet and elaborating on your stance. Many people around these parts would be content with just using a button rather than engage in a debate.
The book and the movie both take place within a monastery, where there is a very clear code of conduct.
Except the code of conduct of the monastery in question (or any monastery) isn't related to how you conduct a professional murder investigation.
Also, the inquisition gets involved on the orders of the pope. The plot does not revolve around some hobbyist detectives, acting on their own volition according to their own ethics.
The inquisition may be involved and this could be used an an example of professional "seekers of truth", but the monks in charge of the investigation aren't inquisitors (or professional detectives, however we may wish to label such activities). They just happen to be there at the time and are asked to find the cause of death, Their involvement is purely accidental, while "some hobbyist detectives, acting on their own volition" at least have some knowledge or background concerning the issue, regardless of how small it could be, so I find your argument to be self-defeating. Evenmoreso considering you were the one saying how the world in that day and age lacked the sophistication to deal with doing any murder investigating.
A murder myster is exactly what it says on the tin: a murder mistery. Having Sherlock or Poirot on hand isn't required to have one, although it certainly helps, because they can give the plot a structure by shaping the flow of the book. However, given the fact that you want some random schmucks to play your game (some of which may have no prior knowledge about crime-solving) it isn't unreasonable to do exactly what Umbero Eco did and just throw some random characters into the grinder and let them try and solve the mystery purely by using their wits/logic.
Even if the murderee was like a powerful noble, chances are that his murderer was also a noble, who probably had him murdered via an assassin. A random peasant offing a knight seems extremely implausible and important people in medieval times generally don't get prosecuted. What role would the PC even have? There were no police officers back then. Seems like a waste of a setting to me, even with a highly liberal dose of artistic licence.
1) Doesn't have to be a noble. Could be a merchant. Or someone close to people in the positions of power, meaning they'd wish to know if they were the intended targets and if so - who wanted to get them killed.
2) Some people could be untouchable (so you could simply find yourself in a position where you will have to go against the grain, should you wish to try and prosecute the killer), but generally murder wasn't a light affair, even back in the medieval times. Combine this with doing the deed without the knowledge or approval of the person ruling the area and this could be enough for doing an official investigation. Or a quiet one.
3) Yes, there were no police officers back then. But if you think that cities or nobles didn't have armed retainers who were tasked with upholding the peace in name of their liege, then you clearly have no idea what you're talking about. So, yeah, you could be such retainer, tasked with finding the killer to bring him to justice in order to make the populace see that they are protected and/or make them see what happens to those who go against their lord's wishes (such as breaking laws he commands them to uphold).
If the murder was premeditated, any half intelligent murderer would make preparations to skip town immediately.
Once again you prove you have no idea what you're talking about, because that's now how it works in real life. Firstly - people are not as intelligent as you seem to think. Secondly - they could think nobody will find out what they did. Thirdly - they may operate with the assumption they are powerful enough to silence anyone who attempts to make the truth known, thereby feeling no need to move (and abandon their land/property/established way of life).
You can theoretically brute force Obra Dinn the same way a pack of monkeys could theoretically reproduce Shakespeare given enough time.
I'd argue recreating Shakespeare is going to take more time. Also, you could say that Obra Dinn isn't really a game as such.
PST's murder options in dialogue only gained any significance by the tactical combat layer already existing.
Nah, you could cut out the whole tactical combat layer and the game wouldn't lose a thing. If anything one could say the player would gain by not being forced was his time to go through shitty combat just for the sake of going through shitty combat (like these totally pointless random encounters when you moved between locations). So either make good combat or cut it. But anyone saying with a straight face that having a shitty combat is good/needed/required/adds anything worthwhile to a game is simply brain-damaged.
Such characterisation is impossible through normal combat where you engage in "battle" not "murder".
I get you don't like doing battle this way, but your statement is simply wrong, because you can have battle via dialogue (as evidenced by Disco Elysium). All that really changes in the manner, but not the deed itself (having somebody killed). Mind you, I say all this as someone who highly prefers systemic/simulationist approach to gaming over narratively-driven one.
Let's all remind ourselves of the encounter with the Practical Incarnation in the Maze of Reflections. There, you are given the option of merging with TPI through sheer willpower, which happens through dialogue. Alternatively, you can fight him conventionally, which happens through the combat interface. If both fighting and merging both happened through dialogue, the distinction between those options would be completely meaningless, since in terms of gameplay they are identical.
Remember what I said about brain-damage? This is a perfect example of what I meant. And I don't meant this as an insult, just to illustrate how stupid this way of thinking is to me. For you
the mere fact of killing somebody in a tactical layer is "totally different" from killing somebody via a dialogue option. I don't care how I kill the guy who wishes the Memorial stone to split when his name is written at the base of it, because the end result is the same no matter what. As a result I am fine with no tactical layer, provided I get enough options to accomodate for the lack of it. Now, the tactical layer as such could matter had combat not been shit in Planescape: Torment (unlike in other Infinity Engine games), but sadly it is.