Newest dungeons in the Game have always provided most of the "atm most interesting tomes". In 2.1 you could get most myth tomes in Hauke and Copperbell, in 2.2 you can get most Strat tomes in the new HM dungeons.

But I agree, this system takes care that "old" (speaking of only a quarter of a year) dungeons will be frequented a lot less after new ones are released. To add to it, the new HM dungeons really are easier than the old ones. The only dungeon I see people struggle with is Ampador HM because of the door mechanics on the last boss. Maybe they took the ATMA books into count knowing players will chase them in masses so they made the new dungeons easy and quick to do.