Item Level should be the first stat people can look at to judge their relative strength, but as is, it's just a prerequisite stat people look at to allow them to enter instances or join Party Finder groups, or compare as an epeen between people with optimal weapons. It does not reflect a character's strength, and misleads players who don't understand the importance of their weapon into thinking that they are comparable to someone with a strong weapon.
It's too common to find a player with a full set of i130 Augmented Ironworks gear and an i90 Zenith. (Or an i100 Atma weapon, which really should be marked as an i90 because its weapon/magic damage is no higher than a Zenith until it's completed and turned into an Animus--the secondary stats added by books do not justify the i100 label at all.)
A player like this will have an item level of 123.
They can technically enter T13. But if they're a DPS, for example, their damage output will be abouthalf or lesssignificantly less than what someone with an i135 weapon and full i120 gear + one i130 ring (also amounting to an overall iLv of 123) can do.
I strongly suggest a change in how Item Level is calculated.
Currently, each piece of gear is equally weighted, as far as I know.
Instead, weights should change to be based roughly on how much weapon/magic damage and primary stats weigh in the damage formula.
I don't have an idea of how much that would be, but I do know that Valk has had approximate formulae for auto-attack damage and weaponskill damage at his site for a long time now. And as far as I know, they're still relevant. Even if they're not, it should be somewhere to start, if the devs really don't have their own means to determine the stats' relative weights.
For the sake of helping uninformed players make better decisions about their gearing progression, and for the well-being of players who know they've been carrying these other people with tiny weapons, I hope the devs can find the time to address this soon. Especially with so many players resubscribing or joining in anticipation of 3.0, and making poor choices in gear upgrades.