MMO's are what you make them.
/thread
hardcore due to the time investment (the 1-60 grind, the R14 grind, and the amount of prep required to raid.. specifically once there is 3+ tiers of raids out)
obviously its not the most hardcore mmo ever made, but its not a casual game in my opinion.
I think the main thing about Classic, is that it is a time-sink (but so was repeatable/world quests) and that its gear progression is much slower than the current loot pinata system, that envelops retail now.
The epic journey, and the logistics behind raiding is what makes it stand out, and sure if investing time into what you do is hardcore, then Classic will be hardcore aplenty.
I think this is a good way of thinking about it. It's as casual or hardcore as you make it out to be.