This has always been an issue and it has to do with how syncing works. Trials and raids are not item level synced, only level synced, so max level trials and raids are synced to the maximum item level of the expansion.

The Singularity Reactor is designed for the gear you wear when you reach level 60 (item level 142). Higher level players sync to the maximum item level of Heavensward (item level 270). You are almost double the item level.

Dungeons are different. Most of these get item level synced after a 40 item level difference. This didn't happen in some previous expansions and it caused there to be a massive difference in how easy the dungeons were if they were all new to it. You can see this problem in Gubal Library (Hard), the Antitower or Fractal Continuum (Hard).