If they have learned from XI in terms of the magian trials and I'm pretty sure they said it themselves, but later on the weapons themselves will be upgradeable so the aspect of no weapon being able to be stronger than relics shouldn't be an issue.

If anything one can hope that later on in the relic's life cycle they allow ways to make them more unique between players or perhaps the relics themselves can take on the form of another weapon. kind of like perhaps the Excalibur could be a relic that turns into a blade focused more on healing/dmg taken and another blade focused on offensive/healing with dmg dealt. It will be interesting to see how relics will evolve in the future or even how they may introduce new weaponry though there will definitely be a long time before we see anything like that.