I can't prove this, but take a moment to consider it. What are the names of the Zodiac grade weapons?

Excalibur.
Ragnarok.
Longinus.

Etc. VERY mythology heavy names. They just gave us these items, do you really think they would discard them in less than six months? I highly doubt it. Excalibur, in general, is huge in the Final Fantasy franchise. That isn't something they would throw out for a weapon that wasn't going to hang around.

At least, that's my feeling on the subject.