I have no idea where the conversation even is at this point, but I wanted to pull this bit out to mention.
I like the change made in 5e, why? Because Alice isn't used to wineglasses being thrown in her face while casting. She's used to being shot with arrows and stabbed with spears.
A wineglass should be easy for her to cast through.
See, I have a logical problem with your last statement. "But the fact that poison was save or die meant that the players would often change their strategy as soon as they knew they were dealing with poison."
See, if I'm running the world, and spider venom is potential instant death, then my goblins (who are sneaky and would prefer you dead rather than capable of fighting back) are going to gather up spider venom for their arrows. Then, they are going to shoot at you from an ambush.
So, when does the party know they are dealing with poison? After they are hit by an arrow, by which point, there is a good chance a PC just died. And how will they change their strategy? They were avoiding getting hit by the arrows before right? And there are problems with things like, hunkering behind cover, because readied actions makes that just as deadly for you.
Or, let's move on from archers with poison. I remember in a few video games encountering giant centipedes. Didn't know that centipedes were poisonous, so your players are walking through a dungeon, find a room filled with centipedes, if they don't know centipedes are poisonous, when do they know they are dealing with poison? Well, that would be after they are bit, at which point a PC might be dead.
But, let us move on from monsters. Traps are a fine tradition. You obviously look out for traps, but you don't always find them. A trap with a poison needle, or a poison gas, or a poison anything. When do you know when it is poison? When it is too late and a PC is likely dead.
But hey, sometimes you do get to see it ahead of time right? You mentioned snakes. Classic movie scene right, fall into a pit of snakes... you are dead. Because you just got potentially bit by dozens of snakes.
So, sure, sometimes you could see the threat coming, and do something about it, but many, many many times, the logic of the situation would mean that you actually didn't see it coming, until someone is already dead.
Yes, but...
If goblins are known to use poisoned arrows, then you would approach potential encounters with goblins differently. There are also ways to mitigate that in game. For example, while poisoned arrows could be very effective, you can gate it behind some safeguards. For example, a critical hit. Or an attack that rolls maximum damage on the die. Or the dosage could be insufficient, granting advantage on the save unless those conditions are met.
After the first attack, where the poison is known, the players/PCs will alter their tactics. Just like they would in real life.
If certain centipedes, spiders, snakes, etc. are venomous enough to be deadly, then the people who have lived with them in their world for thousands of years will be aware of that fact. Sure, adventurers far from home might run across a lot of unknowns but they should also be treating such unknowns with caution. You can also provide some clues to the risks involved if appropriate.
Traps, too. I pointed out the pits in ToH specifically because the traps were designed in such a way to make it unlikely the first person to trigger it would be unlikely to die. At which point, the presence of traps is now known and they can take appropriate actions. Traps have always been a challenge in D&D, because a lot of DMs like to use them frequently. It shouldn't really be a surprise when traps are likely to be present, and in many cases they should be obvious, set as a deterrent.
In addition, traps are often mechanical devices. I have frequently had older traps either non-functioning, because mechanics have rusted, wood has dry-rotted, crossbow strings have rotted away, etc. Or poison has lost its potency, granting advantage on saves, etc.
The point is, if they know that save or die is a possibility, and they aren't sure how dangerous this particular circumstance is, you can reasonably, and believably, give them a way of knowing what the danger is that they face, so they can adjust.
But other effects, like energy drain, are also known. In our campaign, necrotic damage doesn't heal naturally. It requires magical healing, which is also harder to come by. Not all undead cause necrotic damage, but since they can't tell just by looking at a given undead creature, they treat them all with respect.
Falling is more dangerous and deadly in our campaign, as are fire and acid. So they treat them with respect and act appropriately.
Not all of these are factors from earlier editions, of course. But they approach grew out of the energy drain and save or die effects of AD&D.
