No, I mean the ac68, predecessor to the current AC86 (which is already "obsolete" because of AX86), and the ac66_b1, which was a "prerelease" of the ac68...they're old and have been supported for a long time; asus might think it's time to move them to the "legacy" list so they can focus on the newer stuff...and AX88 has supplanted ac88, another one that might be deemed legacy.
...from what I know of the product line historically and currently, I'd not be surprised if asus just stops supporting earlier ac-wireless models (except for maintenance releases) that are non-HND in the near future. it just makes business sense - they can move forward faster/easier when the entire code team is focused on the now and future...think along the lines of Apple: sure the old stuff works, and works well, but look at this new feature, this better functionality...and it's faster and in terms of speed for your money, it's a helluva deal! Also remember wifi6e is coming...that "pinnacle AC-wireless" stuff is ancient in comparison. (hey, I still have apple G5s and a late g4 powerbook that still work and I use on the regular - from my cold dead hands...)