*shrug* WotLK dungeons were tough until everyone outgeared them, which for the raiding population was a few months into Naxx, and for everyone else was when they released Ulduar and rewarded Naxx lvl loot from emblems of .. I want to say "Valor" but w/e it was anyway.
For 80%+ of WotLK lifespan the majority of the playerbase massively outgeared the dungeons and heroics which is why people remember them as AoE spamfests; but on release, and things like the ToC 5 man on release and the ICC 5 mans on release, were plenty tough enough to break groups, or cause multiple wipes.