Likely this is going to be a hot take but I really don't understand what was so interesting or good about ARR designed dungeons, Not going to defend current dungeon design either it's boring, I think at least in DT they had a lot more fun mechs, but the dungeons themselves were the same as previous.
I do agree that ARR dungeons were "unique" but they were very unenjoyable for the most part, I personally don't see many people actually enjoying old ARR designed dungeons at least from the people I know usually complain about them.
I don't think we should have modern dungeon design but also I'm glad that it's one less dungeon where I have to sigh because theirs random annoying mechs... But I understand if you personally enjoy how old dungeons are designed that it's a bit upsetting that the old design is going, I can at least sympathise with wanting more interesting designs for dungeons and things in general with ff14.