I will agree with this. The “Bear Runs” in TBC would be another example to go alongside the AQ Gate Opening of things which should likely be “left in the past” as it ran its course, by design, during TBC. (Wrath and later also have examples of time-gated or expansion pack level gating on things) A LOT of this rare loot, and even rare titles aren’t rare by design(at onset), they’re rare because later design decisions made them inaccessible.
I have no problem with people gaining a new means to access items “lost” to later redesign decisions. I am a little more torn on others, the War Bear Runs for example come to mind. While I would have issue with a “Timewalker” style raid getting them, I am not so certain about how I would feel about someone who did it using the same talents and abilities my groups had, and similar gear “appropriate to the relevant patch levels.”
The other “other factor” in the mix is the “Slippery Slope” matter of “Dates matter” in such a context. Particularly if “legacy players” are given ample warning/opportunity, if for some reason they haven’t logged into WoW and triggered the corresponding achievements on a date before Blizzard allows the stuff to xfer across.
So what if somebody gets an Amani War Bear achievement in 2024, I got my Achievement the day the system went live. People can decide for themselves who has more street cred/epeen based on the disparity between the dates.