Considering there are currently 21 jobs and, thus, 21 Phantom relics, having the the grind proccess being smoothed out after the first one should only be fair for all completionists. This is also why Resistance Weapons also had plenty of one-time steps.

As jobs pile up with each expansion, the multiplier to time investment grows larger and larger, making it a lot harder to fine tune the right amount of time investment per job. Making every following weapon grind about fishing atmas isn't sustainable.

My only caveat is how the reagents for additional weapons don't, at least, have an option to buy with Bicolor Gemstones so that people can still do FATEs in Dawntrail areas after the first weapon, helping the FATE trains stay a bit more alive but, since it's about having options outside Occult Crescent, people can just do Roulettes to get the tomestones.