WoW was never really difficult to begin with. It was new, unexplored, and challenging. There were not a ton of addons, boss mods, streamlined questing hubs, or large amounts of gold in the game. What you remember as "hard" was actually inefficiency. People raiding in horribad gear, or even Pirate hats. No one was Min/Maxing, chanting and gemming was hardly a thing, and the stats on your gear were the stats you were stuck with.
You had hunters running out of ammo, and food to keep their pets happy to keep DPS high, locks running out of soul shards, rogues running out of poisons, and buffs only lasting 5 minutes instead of 60 minutes. Plus, you had to buff everyone separately, not the mass buff we have today. What you remember as "challenging" was actually a new game with poor mechanical design. The design since has only continued to improve the game and remove the tedious technical aspects which were originally introduced. As for getting the "challenge" from a 10 year old game, I wish you luck.