Only a fraction of the developers who worked on Classic now were part of the original vanilla team. And the designers from back then, as in the ones calling the shots, are pretty much gone altogether from Blizzard. So what THIS Blizz has done, is just the changes and the work of porting it into the new Engine based on past logs and the patch they saved from vanilla.
It’s not this Blizz that did a great job. It’s the original designers that did a fantastic job. This Blizz just tried their best not to ruin what the original Blizz accomplished, however there were cost-cutting orders they had to adhere to, which unfortunately included layers (as in they went with layers instead of “unnescessarily” trying to guess how many servers would be needed with the risk of guessing too high), which they also likely wanted to associate to Classic as well since they were expecting it to do well (the feedback weren’t exactly hiding their enthusiasm), which is likely to become a part of 9.0 since sharding is overwhelmingly seen as a negative feature over on retail.
Kind of like creating the hero for a villain of their own creation, and doing their best to associate good press with it in order to raise the positive image it’ll have once it’s announced for retail (most likely).
If they DON’T have such plans, it means they kept saying how layering is “new technology” in the Q&A’s for Classic (even though it’s just sharding 2.0 and further shows their attempts to disassociate layering from sharding), which they had “gone through the effort to develop for Classic”, only to then remove it for phase 2 because that’s what they’ve also “promised”.
In other words, under orders to cut costs (look back to gaming news from December '18/January '19), it doesn’t make sense to spend development effort and work so hard to disassociate it from sharding when giving public statements, to then only have it “disappear” into nothingness shortly after.
It makes more sense for them to make it seem like the “hero” people want, to give it tons of positive PR by having it “save” the Classic launch by saying how it would otherwise be impossible to keep the servers up during the launch (which it would, but it’d be fine eventually regardless, it’d just take a lot more time like weeks or months until the servers would become stable enough, depending on the pressure the servers would have from people trying to log in and level etc. from day in and day out), which would make people associate the positive image of Classic and its “great launch” to the image they’re trying to create for the layering technology.
Which would then be a win-win since it did cut costs by not making 'em open soo many servers when expecting many players to drop off over time (which, for all you know, they could’ve been expecting more to drop off than it actually did, and keep in mind the queues became less prevalent and smaller in size cuz they kept increasing the population tolerance too so it wasn’t only that people quit playing although some have definitely quit playing already, it’s just not the only relevant factor), and it’ll likely garner a lot of positive attention so it’ll become the great “hero” that slayed the bad “villain” of sharding over on retail for the next expansion.
It did however get this big setback of bad publicity with the layering abuses and its effect on realm economies and character progression and whatnot (including the prevalence of rare patterns and BoE drops from instances etc.), so it will not get the full effect of a great welcome they were likely trying to achieve by doing all of this though. It’ll nonetheless still be seen as a great exchange for dropping sharding, if that is what they’ll do for the next expansion.
Also, fun little story, they also attributed the first expansion launch without the need to keep the servers offline, which was the Legion launch, to the sharding technology. Which is the same kind of language used for layering and the Classic launch (not identical, but similar), in Q&A’s prior to its launch. It’s just that the obvious downsides to layers was foreseen by a few, like the layer hopping, which the fanatics kept saying “wasn’t gonna be a thing”, and then what nobody saw coming which was the effect it was having on instances.
Now, Lore did say in a blue post that the bug causing instance resets while inside “was a thing in vanilla” too.
Couldn’t be bothered writing it all again, so there you have it. Try to look behind the curtains instead of trusting what you’re told at face value all the time.
So the dungeon reset while inside just so happened to not only resemble layer hopping, it was also triggered by hopping layers. The coincidences sure are plenty.