To add to this:

The 385 iLvl step removes ALL substats on the weapon. There's an additional grind to get substats back on it and its also a matter of RNG.
So to get to a substat total that makes it actually useful or to get desired stats can take quite a while.

If you are looking for a non-Eureka way of upgrading your weapon i recommend getting the current Genesis Tomestone weapon.
Will still take 4 weeks with the current cap on the crystalloid from O12N but is far less of a grind than Eureka IMO.