The current system isn't perfect, but it's in my opinion, the best implementation I've encountered.

The main concerns that pop to mind are:
- Higher level + item leveled players versus the on- level + possible lower item leveled causing disparity and making runs frustrating.
- Preventing power creep if SE reworked the past-dungeon system and gave us all of our skills.
- The new constant need to make sure the disparity between older and newer players is balanced (which means constant maintenance of older content, taking focus away from future in some form).

The current system of syncing down players means that what the content is balanced around is not so easily broken. Though power creep still exists in past dungeons (syncing you down brings you down to certain stats, but it's easy to tell who has a higher lvl/ilvl during a run, leaving them at capped stats that aren't normally achieved at the level/ilevel the content was made available for), it could be much, much worse. If this is put in solely to "work on your rotation," you have striking dummies for this to work it into your muscle memory. If it's to make sure you have the DPS for a fight with your current rotation, you have the Stone, Sky and Sea for that. If you're looking to optimize in a fight, there's literally nothing better than to do the fight and pay attention to where you have moments where you have to line your utility buffs with the rest of your party, move away/stop casting/turn away and making those gaps as small as possible.