The Changing Bonus to Heirlooms

Heirloom armor and weapons were a fix for a problem that is mostly not really there anymore. See, back in vanilla, you could do every quest in a zone and find yourself without any really significant upgrades to your gear. I think the expectation back then was that randomized green drops and items from dungeons would fill in your gear gaps, but I think a lot of the perceived difficulty of the early iterations of the game (apart from all of us just learning how to play our classes) was that your gear was utter garbage.

Another issue cropped up as WoW released expansions every two years for a decade and a half. The climb to level 60 was originally a big accomplishment, but as our main characters naturally sort of coalesced at the upper levels, it became harder and harder to get a brand new character up to the level cap. Monks, the only class to be added to the game without a major boost to its level, remain one of the least played classes, and I suspect a big part of that is that there's such a mountain to climb (despite being the new hotness in Mists, I didn't remember seeing Monks in dungeon groups or raids until we were several weeks into the expansion.)

Heirloom armor, I think, was primarily created to solve the first problem. But it has also become a staple of leveling new characters, thanks to the boost to experience gained while wearing a full set.

The thing is, today, with 120 level to go through, I actually feel that even with our current pandemic-boost that literally doubles experience gained (on top of the 50% or so you get from heirlooms,) it still feels like it takes eons to get to the top.

And that's why in Shadowlands we're seeing this massive revamp to the whole leveling system.

The thing is, this revamp will be so extreme that it actually makes heirlooms redundant. While I'm sure there will be those who aren't satisfied with only dinging fifteen times over the course of their quests in Drustvar, the system effectively recreates the way that Death Knight worked in Wrath - you did a little starting quest chain and then got sent to the previous expansion's leveling zones, meaning you couldn't just step immediately into the current stuff, but you got a huge catch-up (granted, Demon Hunters were just dumped into Legion, which I actually think worked out ok.)

Because the experience boost is really unnecessary, and in fact might break the experience they're trying to give players, instead we'll be getting new set bonuses for the armor (I believe the weapons will remain just scaling stats items.)

The bonuses will include a burst of damage when you level up to nearby enemies plus a primary stat boost that you can extend as you kill more monsters, as well as some increased out-of-combat regen (we'll see if it's noticeable.) The really huge boost, which actually in practice sort of restores the XP boost, is that the rate at which you consume your Rested bonus XP will be cut by 30, and then 60% as you get more pieces.

So, ultimately, you will level faster with heirlooms, both by making rested experience worth more and by powering you up periodically.

Even though this looks, on the surface, like they're taking something away from players who sank a not insignificant amount of gold into, I think the end result will still make leveling alts a profoundly less tedious experience.