I've played in a competitive raiding guild since near the end of Molten Core progression. The game is LEAPS ahead more difficult than it used to be with regards to what is required from individuals, leaders, and the group as a whole. There is an infinite amount of truth to the statement that players have become much more prepared and researched than our former selves. It'd be nearly impossible to not have improved just by sheer hours put into the game. But with preparedness and increased skill comes the creation of harder content to challenge it. Take *almost* (I used the word almost here) any fight from MC/BC, scale it up to today's level of HP and outgoing damage and watch it fall over by even the worst of active raiding guilds.
Vanilla/BC was A LOT of fun. I had some great, if not the greatest, times playing it but it definitely wasn't the hardest of content either.