Considering we're talking about leveling dungeons, significantly higher accessories that would raise average to be our experimental iLvl requirement for said dungeon just isn't really an issue.
Take for example Castrum Abania.
My recommended iLvl for this is 280.
To have accessories from Lv.68 HQ to actually fill in the right side, you would have had to clear all the sidequests at level. Furthermore, you would still pretty much need Lv.66 HQ gear on the left side filled in to reach an average of 280. These conditions are suitable for running Castrum Abania.
Yes, you may be lacking in Defense and Attack stat from left-side pieces, but it's not significant.
Now, if you have someone running Augmented Scaevan accessories and Valerian (i160 Dungeon gear) armor in order to meet their 280 average iLvl requirements... Yeah, there's some significant problems there. But you also really need to ask "why?", because that would be extremely deliberate. At the very worst, I would expect to see Augmented Scaevan accessories paired with Augmented Shire armor, and that would be a 335 average, and would also be more than acceptable for Castrum Abania.
This is all supposing an iLvl 280 requirement existed for Castrum Abania, of course.
If this requirement existed, these are the combinations I would expect to see.
First-timer: 285 HQ armor, Bardam's Mettle accessories (However, they would probably be more inclined to knock out sidequests for the 285 HQ accessories, rather than farm dungeons to meet requirements). (Functionally 280)
Advanced Shitter: Neverreap armor, Augmented Scaevan accessories (Really need to ask why, cause you have to go out of your way to do this) (Functionally 220)
Advanced Alt: Augmented Shire armor, Augmented Scaevan accessories (Functionally 300)
Common Shitter: Void Ark armor, Ryumyaku accessories (Functionally 240)
Common Alt: Augmented Shire armor, Ryumyaku accessories (Functionally 290)
For "Functional Level", I'm taking the average of - the average iLvl and the average armor iLvl.