Tony, when comparing traits among editions, like lethality, we have to use how the game was designed. Not how you totally modified it.
IDK, it was designed to go to -10, but that seemed to disappear to make it /more/ leathal. ::shrug:: ...and AD&D was notorious for being run very differently from place to place & DM to DM.
And, how the game was designed sometimes just didn't work, it contradicted itself or punted to the DM for a judgement or ruling, making comparison even more fraught. Likewise, there was no helpful CR guide, so if you figured it was fine for purple worms, for instance, to eat 3rd level characters with regularity or whatever, you'd have a much more lethal game than someone who reserved those for deep/high-level dungeons.
You start running 5e without regard to encounter guidelines, you'll get all the TPKs you want.
A single breath weapon attack from a red dragon in 1e would kill half the party at name level even if they made their saves instantly. A couple hits from a vampire would reduce the most stout name level PC to nothing. Magic resistance as a % rendered casters almost worthless. The list goes on.
Those all seem like over-statements, to me. They might be OK, if you made a number of assumptions, fairly meh stats, exactly average hp rolls, no magic items that in any way help, a Huge/Ancient dragon, etc...
Some quick math illustrates just how big a difference it makes to be able to cast lower spells at higher slots, and why Tony's dismissal at that point is either ignorant of the rules, or disingenuous to the argument.
You don't /need/ to insult me to register disagreement. Just say'n.
In 2e, spells scaled with class level. In 5e, with slot. The former is much more powerful, in general...
If the cleric maximized on healing spells, this is how much damage they could cure once per day
Is not hugely relevant. Yes, 5e Cure Wounds scaling with up-casting theoretically lets you burn every last slot for healing. 5e also scales hps & damage more rapidly than 2e so that scaling is called for. The same was true in 3e, by the simple expedient of having a healing spell at every spell level.
But, ultimately, if you're putting your whole slate to healing, you're not in the middle of an adventure, you're on to downtime, and you'll prep & cast as many full slates of healing as you need.
5e spontaneous casting, though, /is/ a more valid point. If a 5e party does get unexpectedly pasted, the cleric /can/ burn slots on healing like crazy, he didn't have to prep all his 1st, 4th & 5th level slots specifically for that purpose, that morning.
this illustrates another key difference where 2e was tougher: In 2e, your stats didn't keep going up.
They didn't go up with level, there were items that could boost them, though some radically while you had the item, some incrementally but permanently.
The scaling in the two games was different. Attack & Saves scaled more quickly in 2e, hps/damage in 5e.
...anyway, perhaps more cogent, to make 5e feel more lethal:
Stick to lower levels (in particular, replacement PC start at first regardless of the party average level).
Toss the CR guidelines: feel free to use higher-CR monsters and to outnumber the party.
Feel free to narrate death the same way you would success or failure, numbers notwithstanding. You don't have to add-back SoD to kill a PC with a trap, you just describe the results of an action as a trap going off and killing him.
Don't pull any punches.
