I think if a player is lvl100 and still goes a lvl 20 dungeon or something really low, he should be allowed to use a few more skills of his whole set. Similar to how crossskills worked previously. In lower dungeons you were able to use like 3 out of 10 crossskills. In max level dungeon you were able to use all.
Just another category in the action menu 'synced' where you can select them. Let's say he is allowed to use 3 more abilities in sastasha, but each fit a certain category like offensive, defensive or support - so players are prohibited from just using 3 damage abilities for the lowest dungeons. This would have to be on a job to job basis, which one are allowed specifically for synced - as some wont make sense.

Dungeons itself are however already too easy. And this on SE.... I think the player damage output is less relevant, when the damage received is already so low, it will never put you in any trouble....
They can probably increase damage taken by 100% in most low level dungeons and it would be just fine.

Maybe upon entering the dungeon, players being able to set dungeon modification, that make the dungeon more difficult when starting it (damage, healing, HP, amount of mobs, random mobs, no sprint, random cc etc. - modifier) - while at the same time unlocking 1 more slot in the synced category for each detrimental dungeon effect picked.

but they will probably never do something like that, because it would break their trusts and squadrons scripting