its really the opposite. the coil/ soldiery weapons are offered as alternatives to grinding for the relic. the relic itself is very gil/time consuming on an insane level, and is not soemthing everyone will do. coil weapons are offered for the people who dont want to have to do that for a good main/off hand. soldiery weapons are good as well, but they can take some time. on paper, coil would offer a good weapon with minimal effort as compared to grinding for the soldiery, soldiery is for the people who dont mind the grind, but cant complete the coil(like me). i have lv 110 main/off hand for my lv 41 pld.

the soldiery/coil weapons appeal to two different groups, soldiery is for people who dont mind the grind, and coil would be for the people who dont want that kind of grind, but can still put in the effort.