The beta version of WoW: Burning Crusade Classic has been online since yesterday and is - as is normal for beta versions - full of small bugs, construction sites and inconsistencies. For example, some testers quickly noticed that they receive surprisingly few experience points for killing enemies in Outland.
This is particularly noticeable in the first dungeons of Hellfire Peninsula. A run in Hellfire Bulwark or Blood Cauldron rewards just shy of two "experience point boxes." But enemies in the open world are also stingy.
And indeed, players have dug through their old screenshots from 2007 and found confirmation there: Enemies in the TBC Classic beta give fewer experience points than they did back in the day.
For example, a defeated Suffering Giant from the Zanga Marshes in the beta currently rewards 367 experience points (not rested). In 2007, however, it was 513 experience points. Such a difference naturally adds up to a significant amount over the entire leveling phase. According to one Reddit user, the difference could be due to the fact that the beta still uses the Azeroth formula instead of the Outland formula to calculate experience points. He also proves this in the just linked post with a calculation example.
At the latest when Blizzard makes an appropriate adjustment, we will know that the players are right. Currently, by the way, beta testers level the fastest via quests, which could be a problem in view of the potential player rush at launch. Whether this will change through an adjustment of the formula, we would have to wait and see.