Players were not as experienced back then.
When dungeons first came out they were chaotic 'class raids' where you'd take one of each class along so they could each get their dungeon loot. But then they locked most of the down to just 5 players.
I remember when I first saw a hunter use traps and pulling - it was a revelation.
Towards the end of classic one of the quests to upgrade your dungeon tier was a Stratholme speed run, the forerunner to challenge mode and mythic+. All things that have basically trained us to be better in 5 mans.. I'd be shocked if dungeons didn't feel easier.