I'm actually shocked to see that there are people that want immersion breaking mechanical equations, functions and logic gates thrown into their face. I agree with what you are saying but the perfect ruleset for this already exists in 5e and what you are seeing is Larian having taken liberties with the system, chosen to not implement it for whatever reason, or actively wants the presentation of their game to include these artificial arcade game features for whatever reason.
Yes, this thread is suggesting / feedbacking on that decision of theirs. Saying D&D isn't immersive because it has immersion breaking components of decisions, logic gates, and mechanical equations is an odd paradigm to start working from. Its only immersion breaking when you don't feel its something you should be doing or you cant do it when you feel like you should be able to.
In 5e passive perception doesn't automatically trigger situations. It happens in the background. It affects the initial description of the area once you enter it and any desire for details ot a more detailed analysis requires you to roll. This works in tandem with the investigation feature.
Passive perception is what the average roll would be if you rolled infinite times and it is there to stop someone saying "roll for perception!" in dungeons and rooms to the DM. You can, at any point of the DM describing things, say "Id like to look at that statue, specifically" - even if passive perception had picked nothing up. Its a useful mechanic to avoid dice spamming from a PC.
As for illusions again passive perception will let you know immediately that something is wrong with a certain object but it still requires interaction to 'dispel' the illusion. In this case you do not need to roll anything but simply interact with the object to break the illusion.
Illusions require an active intelligence(investigation) check equal to the DC to see it as such; there is no mechanic for passive investigation due to the nature of what investigation is and how it is applied differently for each situation. They have done a good job of letting illusions be illusions, however. Ive been able to walk through every single one of them without any prior clue (except the map) that there is something beyond.
This is not how things currently work in the game and I honestly haven't seen anyone make a convincing argument as for why they have deviated from this formula and these rules other than they are not aware of them, or consider their current system superior. In the case of the later it makes me question this full price EA and the point of giving feedback as it should be whichever system we as the players consider to be superior that should take precedent.
It feels like they have it almost perfectly wrong, at the moment. If they just rotate it a bit and put in more player controlled activity - a button that does a perception check on a small area, or investigation check on an object and lets us try until we hit a DC high enough to trigger "This is something / This is not something" then people can be as OCD as they want about it. In my last multiplayer game we went to the church with the resurrection skeleton guy. We all failed our checks to find the keyhole to his crypt. We had to leave. There is no other way to get in there or find that keyhole that we could think of. So, now we can't resurrect dead companions. Wtf. We need more tools than passive stats when it comes to some of the most used and highly rewarded mechanics in the game. Yes, it is a bit of a chin-scratcher if Larian decides to throw all of this advice out the windows, for sure.
