The leveling experience for the Burning Crusade and Wrath of the Lich King levels of 60 to 80 has been greatly reduced from 6,689,030 XP to 4,412,600 XP which is a reduction of 34%. This has been a notoriously lengthy leveling section, and this reduction will be very noticeable and appreciated by those players leveling new characters such as those allied races!
That’s because armor of higher level has higher Azerite power requirements than lower level armor. That means a shiny new piece of Epic gear will have better stats but, unless you’ve been diligent about your Azerite power grind, won’t have as many traits unlocked. You lose options as you earn better gear. Eventually, you’ll grind out enough Azerite to earn those traits back, but you’re left with limited customization until then.
Heirlooms: Heirlooms are the best source of bonus XP for leveling. All slots can be gotten pretty easily now, except the rings. The time you need to spend to get the rings if you haven’t gotten a level 3 shipyard in WoW is way too long, so getting the rings is generally not worth it. Having all your heirloom gear will boost XP by 55%. Generally, you want heirloom gear with crit on for leveling as you want to kill mobs in a few hits as possible
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing YMMV