From reading your post I get the impression we've got on to talking about normal ADOM vs normal Diablo... Adom is a far, far harder game, I never disputed this.
The comparison I was drawing was *ironman* diablo vs *eternium man* ADOM.
I assume you already know what eternium man involves for ADOM.
Ironman diablo is playing through diablo 1 as a 3-man team (usually warrior/rogue/mage) without ever dying, starting a new game, or entering town... You start the game, spend your 100gold, then enter the dungeon, and don't leave until you or diablo is dead.
In practice completing eternium man ADOM involves nothing more than either farming with your pet, or just waiting to get lucky. Eventually, after enough tries, a monster will drop a RoDS, after which it's a simple gremlin bomb into wish engine. It's pretty easy, just takes a while (and a few tries) for a RoDS to show up.
I don't have my FLG, because I didn't consider it much of an acheivement. An eternium man FLG only proves that you got a lucky drop.
Completing ironman diablo takes a lot more than a lucky drop (though getting a pool early certainly helps).