On top of the lack of duty hard sync for endgame duties besides some dungeons that DO have them (and are already a lot better as a result), there is also some serious creep coming from multiple sources that stack on top of each other, and the more they do the older the content:

- Potency powercreep, as job toolkits gained more and more over time, even if they try to conserve older power levels a little with traits like melee mastery etc.
- HP/defense powercreep, which comes from various changes they did like the removal of belts, main stat changes on tanks, removal of primary stat materia, etc. For example if you go in MILNE in older savage fights in SB or whatever, you'll somewhat massively overtake the older HP values of their time.
- Sync stat powercreep, since level sync progressively fills up substats until they reach their max values the higher the difference of the content ilvl with your real item level.
- The battle system has changed a great deal. A lvl60 endgame duty in HW had you with full 3 hotbars of skills (and more complicated jobs and party team play than what we have today at max lvl) for example. Older duties feel easier as a result because the onus was not completely geared toward encounter mechanics alone.