Regarding Heavensward content available to the new player:

As we know, to play Heavensward's content, one must complete A Realm Reborn's main story questline through Patch 2.55. ARR has been adjusted so that new players will gain double the experience points in the main story, making side quests not needed quite as much, and the Duty Finder prioritizes new players in the queue. The option to remove item and level sync in dungeons was also introduced to help new players, so that dungeons could be completed without an entire party.

Item rewards in ARR content also offer better gear. For example, quest rewards that were item level 55 before, can now offer ilevel 90. And by completing the Chronicles of a New Era quests from patches 2.1-2.55, players can easily get a full set of gear that's item level 110.