The level-cap was quite a challenge in Everquest. Which is also _the_ hardcore PvE MMO. Maybe start playing that one, it is free2play now. Vanilla WoW is child's play compared to EQ.
Besides I just remembered that there are vanilla WoW servers, so if you love it so much, why don't you play vanilla? But as GP said, vanilla WoW wasn't very hard. The endgame content basically only needed tons of grinding (and an immense pain-tolerance because of all the bugs). Scholo, strat etc. hard? Only if you have terrible equipment, but that.. again.. can be fixed by just grinding.
In the end all "challenges" in WoW can easily be beaten by investing more time, and it has been that way since launch.