It's good (or at least, not bad) that you have to do Coil to get Sands, Oils, and Unidentified Tomestones. It's even alright that you (apparently) have to do Turn 7 and higher, instead of just Turn 6.

But it's really, really bad if you only get one of each (of two out of the three) item per week, and have to split it between the entire party according to RNG. It shouldn't be possible to clear Coil every week for a month and get nothing for it, but that seems to be exactly what's going on here.