The Life Drain ability of course. In an edition where most most effects do Hit Point damage and some status effect that usually translates to Disadvantage, reducing maximum hit points is a large impact to survivability.
The 3e Wraith played the same role, CON ability score damage in combination with damage ‘twas very potent. Many a PC and monster succumbed to the combo in my experience.
In either edition the Wraith was something that typically hit above it’s CR, due to sucking the life out of a PC.
Now If you feel the 5e Wraith is weak compared to the 3e Wraith in reference to their place in their respective systems, I would be interested in your thoughts.
Not even close, from your reply I'm thinking you underestimate either what it took to remove in 3.5 or massively overestimate what it takes to remove in 3.5
Hopefully I don't need to go over incorporeal traits
again.
The 3.5 wraith was almost guaranteed to hit your tanks because of that, the only people who had a reasonable chance of avoiding it for more than just luck were dex types who were usually rogues & rangers lacking in co as well as fort saves so whoever was probably taking them was doing it with roughly mage armor+dex at best or close to touch ac.
Now getting rid of those 1d6 points of con damage, you recovered
one point per day or 1d4 points with lesser restoration. Greater restoration was a 5th level spell that could recover all of it sure, but because everyone who had either needed to explicitly prepare X many uses of it you couldn't just prepare it & use it if needed like now those were even more significant
In closing on the 3.5 wraith, a character with very high con might have con in the low to high 20's while having hp in the 60-80+ range so that 1d6 was chipping away at a much smaller pool where you simply died if it reached zero. Not only that is because con bonus applies each level getting hit for an average of 3.5 (lets say 3) meant that a level 10 character was losing 10-20 hp from con damage alone each round & even
if they hit the wraith still had a 50% chance of doing nothing on that attack. Not only that, because it's targeting con you have worse and worse odds of saving the more you go. Because of that it wasn't uncommon to be more afraid of being killed by con damage with lots of hit points left.
Now
the 5e wraith. It's not ignoring armor so that +6 to hit vrs just plate & a shield needs to roll a 14 or better. Yes 4d8+3 averages out to a similar number of hit points lost, but it's only target it hp & you've got gobs more hp than con.
Not only does the wraith have very poor odds of hitting in 5e, but it also no longer causes a death spiral to build as those hits land. You no longer need to rest one day per point either, get a
single good night's sleep & the lifedrain is
all gone in the morning.
There is also the fact that it's necrotic rather than ability score damage so any necrotic resistance halves the damage it does when it
does hit in 5e. You also only need a magic weapon or elemental damage to ignore resistance & don't have the 50%miss even if you hit
a creature that imposes "we should take a long rest to let everyone recover all of their hp damage and recover all our spell slots plus maybe nova those a bit more if we see them again" isn't scary... a creature that can quickly impose "guys we need to spend a week plus recovering con damage but can maybe get that down to two or three days if someone can prepare lesser restoration a bunch after the first... do we have
anything that works better than mage armor if we see more?" is
Rust monsters... various oozes, trog stench, everything with level drain, stuff with nasty poisons, & probably lots more I'm overlooking that did ability damage & other save or suck/save and suck/suc/save or lose abilities, etc all got similar defang'ing treatment in 5e