I get this. My comeback, though, is that while mechanical setbacks always matter, story setbacks only matter sometimes; and even then maybe not nearly as much.
Further, a mechanical setback is (with exceedingly rare exceptions) immediately obvious to both player and character as soon as it happens. A story setback might not be obvious at all at the time it happens, in that the players/PCs might not realize how important something is or was until much later if ever. (the game I'm running right now is a perfect example of this - they've hit a staggering setback in the story but don't fully realize it yet)
You did, and they're quite good.
But, what would be the player response were you to try to add them into your own game next weekend? Then, consider the response you'd get had they been present all along and you now decided to take them out.
That's the difference
@overgeeked and I are talking about.
If I were to add them in right now, they'd hate it. Most of us didn't use things like level drain back when they were in the rules. Which is why I would never do that to them, even if I personally liked level drain. In my group, we're perfectly adept at challenging the table, including high lethality, without using level drain (et al).
However, if for whatever reason they were waxing nostolgic and talking about the "good old days of level drain, when things were actually a challenge", they'd laud me for bringing it back.
I mean, we've literally had post-game discussions where the players offered feedback like, "the fights are getting a little too easy, can you up the challenge?" And shockingly, the players didn't complain (except in jest) when the challenge was increased, despite that characters were much more likely to die as a result.
RPGs are a group activity. I'm literally scratching my head at how you imply your players behave. You kind of portray them as a bunch of children who only ever want to win even though that would ruin the game for them, and you the stern parent who forces unpopular challenges on them for their own good. IDK, maybe I've gotten the wrong impression? It just seems like an unhealthy dynamic, if I am in the right ballpark.
Indeed, as has been well-documented here and elsewhere; never mind my own memories of my 3e DM swearing at the rulebooks now and then over just this...
And the question then becomes, if an encounter's path and outcome can be that closely predicted, is it even worth bothering?
And in the case of an experienced DM, I agree.
But where does that leave the new DM other than learning by trial and error (which some here seem to strongly dislike as a learning method)?
Yes, it's worth bothering. The d20 is a fairly swingy randomizer in most circumstances. Having played plenty of 4e, despite it being the least swingy there was indeed significant unpredictability. Encounters could most definitely go against the players. Failure was on the table.
As I've said before, in the case of a new DM it's better to have the system default to easier encounters. That way they don't have to worry about accidentally slaughtering the party while learning the game, and can focus on having the most fun possible. Having run for a lot of new players in the past few years, I assure you that newbies do indeed find the default encounter guidelines challenging. It's those of us who've been playing for many years who find it a little under tuned out of the box. Fortunately, we have the experience to season to taste.
Including anything in every adventure gets boring rather quickly. I intentially try to mix up adventure types and focuses - one might be undead, the next might be giants, the next might be a mystery, and so forth - both to keep it fresh and to give a variety of chacracters a chance to do their thing (if they're in the party at the time!).
In the last seven adventures I've run, level drainers featured prominently in one and as a sidelight in another; if memory serves, two levels were lost in total. It's much longer than that since I've had anything appear that had a major aging effect to it. During those seven, one PC did lose two limbs (both his legs at once) through some bad luck; and through an intentional enemy effect another was permanently poly'ed (non-dispellable) into a giant ant - and took a crap-ton of really nice and expensive items with her. There's also been (I think) 6 deaths in total, of which three came within the last real-time month in a back-to-back pair of very tough boss battles where they did well not to lose more.
So, summing up: that's 6 (deaths) + 2 (x levels) + 2 (limb losses) + 1 (perma-poly) major Bad Things over seven adventures. There was also one very major item loss - a Bag of Holding recently destroyed when hit by a lightning bolt; all its contents went with it.
They've also got stinkin' rich over that run, picked up some hella nice items, and have been able to undo all but three of those Bad Things: the Bag-plus-contents remain lost; one dead character who declined revival, and the perma-poly.
Other than brief blips, the party size has been unusually consistent at 6 throughout; with the perma-dead one and the ant replaced on the fly. Level started at 4th for this run, last night the first one got to 7th with the rest mostly 6th.
Eleven "bad things" over seven adventures. Six of which were deaths, so that's 5 "perma bad" things over seven adventures. I presume the level drains and limb loss each took place during their same adventures, so that's 3 instances of "perma bad" challenges over seven adventures.
Therefore, clearly you don't NEED these mechanics to challenge your players, if these only featured in something like three out of seven adventures. You might like the variety that they bring to the table, but either more than 50% of your adventures are without challenge or you're able to challenge the party just fine without level drain (et al).
Again, I'm not arguing that there's anything wrong with using those mechanics if your group is on board. I'm simply refuting the concept that a group cannot be challenged without resorting to them.