I highly recommend actually staying in the 20-60 range zones until you ding 62. The reason for this is that despite getting a slight penalty in experience for being over-level, the advantage of having flight will more than offset this. That, and WOTLK and TBC zones are the slowest part of the leveling process. Minimizing your time there as much as possible is worthwhile.
A "stat squish" and "item squish" was implemented to lower the numbers used in the game, e.g. a legendary item previously with a level of 1000 reduced to 265. Unique class-specific buffs are added back, i.e. mages' Arcane Brilliance and priests' Mark of Fortitude. Titanforging—a random event that raises the initial item level of an item gained via drops or rewards—is still in the game; however, if the item is one of those affected by the Heart of Azeroth, then that item cannot be titanforged.
Some dungeons are also much better than other. Some take a long time to finish and some are quick. Some have few quests and others have many. The ideal dungeons have a lot of quests and are quick to finish. If you are sent to a long dungeon that you have already completed, you can leave but you won’t be able to enter a new dungeon in 30 minutes. Dungeons like the Stockade are super quick, so it will still be good XP if you are sent here more than once.
Essence Font should only be used to get the HoT effect out in order to quickly burst single targets through the double Gust of Mist hits. Cancelling a cast of it when your party has the HoT effect rolling on all of them will allow you to use Mastery-proccing spells faster for burst healing on any target that needs it. However, continuing the channel can be the right call in specific situations, normally when you need group healing while you yourself are moving. It depends on the situation at hand.
But the system offers a painful and mindless grind. At worst, it feels like a cheap and artificial wall blocking you from playing your character to its full potential. Levels of your heart come fast at first, but the costs become prohibitive when you get up into level 20 or so. This wouldn’t be an issue if the most powerful Azerite gear didn’t require reaching level 22 to unlock even 75 percent of their full damage, leaving players left out of features from gear they’ve already collected. This means more grinding.
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 monk...so...yeah. YMMV