I’ve read both Tomb of Horrors and Tomb of Annihilation (and played ToA) and I much prefer Annihilation.

Tomb of horror is a death trap, you are comparing a dungoen that is a death trap to a dungeon that is an actual lair !
there is a clear difference between death traps and lairs. if you dont like death traps then of course the dungeon for tomb of horror will seem badly done.

from the 5e book there are numerous different dungeon types..

Death traps = made to kill players. aka prison like or maze like with no real way of escaping.

Mazes = generally to hide something or lose people you don't want to see.

Strongholds = castles or the likes, places that are fortified to protect someone of importance.

Plana Gate = a place of great importance where deities or their minions can be summoned or conjured.

Vault = good old fashion tresure room, well protected and usually well guarded.

all of these are very different dungeons.
you can't just compare each of them against the others, as they are very different in their motivations.
tomb of annihilation isn'T a death trap, its literally a lair, a stronghold.
what would be a death trap is the bbeg capturing a player and then sending him into a room designed to just kill him.

tomb of horrors is also a mega dungeon... its a campaign in a dungeon all by hitself.
imagine if tomb of annihilation was hapenning inside the last dungeon at all times, no jungles no cities, nothing... you'd have had a very different experience out of it.

as for liches.... their life force starts to wane if they don't kill people on a daily basis. since people tend to avoid liches and their goals, it is normal to sdee liches decrepit over long period of times. but thats why acererak decided to create the syphon which kills people of the world and bring their life force, soul, to him. that way he get a sustainable source reguardless of where he is.

All those are reasons why I liked Tomb of Annihilation so much better than Tomb of Horrors.

Quote from Golaryn >>

D&D Lore is a muddled mess of inconsistencies and retcons.  It is best to define the lore of your game world yourself instead of sifting through all the various editions and trying to piece it all together.

 I just never moved on from 2e. I just kept updating things to the new rules (skipped 4e though), but kept the rest the same. The rules we played by changed from edition to edition, but the setting and cosmology I use didn’t. Keeps it much simpler this way. Pick whichever you like and use that. The rest falls under the “pirate code adjacent” category for me, more “guidelines.”