Atimus = require time, not much RNG since step 1 is shorter step. Mythology is 100% thing.
Mirror of Whorl = base on RNG.
S tome weapon = base on your skill. If you can win it 8 times with your static, it is likely you get one.
Hi-Allagan weapon = base on your skill. But it may need more or less than 8 times, so I can say it involve RNG also.

Basically, if you have time doing boring stuffs, then go for Zodiak. If you think you are such a great in skill since you complain about "lack skill requirement to get", then go Hi-Allagan weapon.