Yep, and given that I play by the rules, Perception isn't overvalued relative to what it sounds like it going on here. So they don't tend to take Observant nor ask me to have their animal companion improve their passive Perception. It would not be as valuable in my game as it is in a game where Perception is always-on radar outside of combat.
And in all our campaigns, observant was taken exactly once by one character, because if fitted the personality and background of the character, and it was not a problem, because the player did not abuse it.
Why is one PC out of multiple PCs not being surprised very often a problem? (Do you ban the Alert feat or weapons of warning?)
We simply do not use weapons of warning, because we think that things that give an absolute power are usually a mark of bad design. Giving advantage is relative and fine. As for alertness, our players realise that it's a stupid feat again because of that "absoluteness" and no-one has ever asked to take it.
Why is noticing traps a problem?
Because it more or less invalidates the whole trap / exploration process (as well as secret doors), and at least one of the resources for exploration just go away, as well as the possible cleverness of thinking about it in the first place. Yes, I know, you can always design special workarounds, but doing it every single time has at least two drawbacks, that of requiring over-design and that of frustrating the player. As our players understand this, they don't try to bend the system back to front to get silly advantages like that.
Just noticing the trap doesn't resolve every challenge. There's still the matter of figuring it out and disarming it, or at least circumventing it. So go ahead and invest in high Perception. It's no problem for my game. Further, does being in the position to notice traps and avoiding surprise have no risk or trade-off in your game? If not, why not?
Because it detracts from the general fun, including that of other players.
As well, having optimization in certain areas and having it make sense for the character isn't necessarily mutually exclusive. Your objection seems to be based on skillful play more than anything and there's nothing that requires skillful play be divorced from entertaining characterization.
The game is a mix of a lot of things, but cutting out whole pans of things just because one player abuses the system is not for me the best way to go. Especially in this case since it's clearly an abuse, so for me it's way better to prevent it at start.
If the way the world is portrayed and actions resolved in that world make it such that passive Perception is a great advantage to have, wouldn't it make some amount of sense for adventurers living in said world to strive to be as perceptive as they can be? Why is this perceived (heheh) as abuse and not natural selection in the context of that fantasy setting?
Because natural selection does not work on individual cases as a general principle, it's statistical over generations of random mutations, for one. Second, it is abused, because the player is bending rules backwards (in particular the help action) to try and achieve something that the rules don't allow.
As for the world being made in a specific way, if it was that way, then ALL characters classes would have expertise in perception, otherwise no character would ever survive if he did not have that.
Observant is already a feat, and a powerful one, and one could argue that it's effectively already giving you advantage on passive perception. It's good enough, no need to double that, especially with bounded accuracy.
This reminds me of a player insisting that his owl familiar should have passive perception of 18 on the sheet, since it has 13 and advantage on rolls using sight or hearing, conveniently forgetting that some rolls might not be using these senses and that the owl, in the dark and even with darkvision would have disadvantage therefore cancelling the advantage. That's the part that bothers me, people with selective reading capabilities...
