Why is Undying 'hidden'? Shouldn't the hex be announced when activated?

That’s true, but who runs Devour Hope with Undying?

In most scenarios you should be able to deduce that Undying is active, but there are a few exceptions which is ok.

Most(If not all) aura reveals in the game don't tell you that you're being revealed so why would undying be different?

A hex notification for undying likely doesn't exist, because it doesn't do anything directly to the survivor. Retribution for example only notifies survivors when the person cleanses a totem and becomes oblivious, but the hex perk also aura reveals when a lit totem is cleansed.

It's the same reason Blood Favor has no hex notification.

All the other hex notifications are because the hex totem has a direct affect on the survivors.

Ruin notifies survivors when they let go of a gen to let them know why the gen is starting to regress.

Devour Hope, Haunted Grounds, and NOED notifies survivors when they are exposed due to the perk

Lullaby only notifies when survivors get a skill check when the perk has at least 1 stack.

Third Seal notifies survivors when they become blinded.

To be fair, I dont know if Retribution does provide information. Because so far, everytime someone played Retribution, I cleansed a Dull Totem before and it made me Oblivious and gave me the information that a Hex is active.

The only thing that might be problematic for the removal of the Aura Reveal from Undying is that the Perk would not do anything on its own (as if you only run Undying and no other Hex-Perks) in this case. But I guess that will be ok, but if the Devs want to keep an effect, it should only light up Auras when cleansing a Totem.

Bloodwarden and lightborn are fair points. The others I'd argue that the aura reveal is a consequence of the effect. But undying, as with lightborn and bloodwarden, had no point in giving aura reveal. It's an additional effect, not a consequence. See what I mean?

Killers do get notifications when Survivors are using perks; DS and Breakout both alert you in the bottom right corner, and more perks should have similar alerts.

However, that doesn't add or detract from the topic at hand. Hex: Undying shouldn't get an alert just because Killers also get alerts, and it shouldn't not get alert if Killers didn't get alerts.

It should get or not get an alert based on it's own merits.

Because it's not hexing you directly, so why should it tell you it's moved a hex? Even if it was after it's tripped by removing another hex, what you're REALLY asking for is an indicator that tells you if you need to/should keep looking for totems, or if it's safe to ignore the rest to work gens. That's asking for quite the advantageous handout, don't you think?

By this logic, Killers should be told if Survivors are running perks like dead hard and/or PT as soon as they become active, so they know who to avoid or down first. It removes part of the gamble that's supposed to raise and/or create tension.

I actually agree for consistency, wouldn't like to see it when just passing a totem but for sure after it's revived a broken Hex

The main disadvantage of the power role is map presence and information though. Survivors are intentionally at an information advantage, even ignoring the existence of SWF.

That said, I don't agree that undying needs a nerf. A big problem overall with hexes is their output is very inconsistent and undying lets you remove the gamble of the hex for a relatively 'standard' effect at the cost of 'downgrading' your hex from a mega-efficient but risky 1 perk setup to an extremely powerful and consistent 2 perk setup. Killer perks should generally be more impactful than survivor perks, as undying-ruin requires the killer to make sacrifices on their loadout. Undying is actually at a really good spot as both a detection perk (Unlike other detection perks it doesn't completely obliterate stealth as a concept at certain points in the game, but its value is still consistent due to it defending totems 'weakly,' and you generally can assume some value out of it) and as a totem defending perk due to how it specifically only interacts with totems that you don't NEED to clear, but if you decide to clear them it doesn't make it impossible so much as take up a more consistent level of time.

The existence of undying-ruin as a super meta-combo more raises the question of if killers need more regression in their base kit (they do) than undying being too strong. It isn't unbalanced, but its such a huge difference maker in stalling the game that shows that killers sorta need more rewards for applying pressure. Perhaps a mini-pop in their base kit so kicking gens is more rewarding and survivors aren't able to do a gen under their nose 4v1 in certain areas with certain killers. Killers are sort of stuck right now with some necessary utility locked in perks, and while this isn't terrible (because different killer powers care about different things) the perk loadout hardcore biases to some detection utility and then ruin-undying, simply because its the most consistent regression combo at the moment but you can't actually nerf regression because its so vital at the moment.

Strawmanning doesn't change anything. You're whining because you want to know it's there so you can hunt it down and not have to wonder. That much is evident. Given someone else said the same, more concisely, and you answered civilly, I have to assume you just don't like getting called out flat on your crap.

As to your "motives", they're pretty obvious. You're entire statement is questioning why you don't get a free handout via notification, which I answered, as well. The notification tied to hexes is intended to tell a player they've been cursed. As the player isn't directly cursed by Undying, it stands to reason there should be no indication of it's presence.

This means you 1) think it should tell you so you can actively hunt it down to stop it or, 2) want a heads up before you get too close to a totem so the killer can't use it's aura tracking to find you until it's too late. Both are nothing short of asking for a handicap.