It seems a hotfix has arrived and removed the ability to lock experience at level 70 and above.
While there hasn’t been a public announcement of this, the support article related to the issue was updated recently to the following:
It is not possible to disable experience gains in WoW Classic.
In Modern World of Warcraft, only characters level 69 and below can disable their experience gains.
In Cataclysm Classic, only characters 59 and below can disable their experience gains.
Visit Behsten in Stormwind or Slahtz in Orgrimmar to turn off experience gain.
Many players have been reporting that the expansion’s scaling was a little strange, and it seems some were taking advantage of it and locking their characters at 70 for some extreme power gains. Blizzard seems to have put a stop to this now, and XP locking is no longer possible for 70+.
