Well, we aren’t given a choice, when the one slowing sceptre also is the one with the best dmg output.
So many times I see it being said that “sorcerer is useless without fulmi”, meaning without slow powers. So to draw the sting (ahem) from that: put slow on an easier to find item.
I guess my schooling in the era where you didn’t “need” to farm only one location taints my view of this. In general I hate the idea of there being only one source for almost every UT causing repetition to farm your desired item. Seemingly Deca kind of acknowledges that, if their putting UTs in event chests is anything to go by.