And the ultimate counter to any argument about weapon level is things like Soboro and Viking Axe's.
Both of which are worse than AH-able items 25 levels later? That comparison isn't going to do much to soothe worried relic holders.
A naked MNK is (most likely) going to see a base damage improvement of 12 points by the time they hit 99 (and almost certainly at least a 10% delay reduction as well). Every other DD job is going to see a comparable improvement, or everyone is going to be a MNK at 99. That gives us a pretty reasonable baseline for what normal
level 99 weapons are going to offer.
So, yes, because h2h damage is pegged directly to skill level (and hence job level), and because there will be at least a pretense of job balance 76+, weapons will
get better than they are now at higher levels, and relic weapons with their current stats will
look increasingly less appealing at higher levels. Only a very significant alteration of game mechanics (which is needed regardless, but which I personally doubt we'll get
) will change this.
Which leaves us with what SE has already told us: relic items will be upgradeable to maintain their value. In a fair world, the upgrade will be simple and painless after all the expense of getting a relic in the first place. Whether that happens remains to be seen.