Well i guess it's about preferences. I for one like to get other slots than the weapon free for more useful stats than perp cost and BP delay. sure, you can switch gear before, while and after executing blood pacts. But i prefer less gear swapping, while still maximizing effectivity.

For you it will probably not be worth the effort, given you are having multiple mages. But I am just playing SMN and WHM on the mage part and I don't really bother getting the cure potency staff, since i have enough potency without it.

It's really all about choices, I like the perp/bp delay staves, because they give me room to improve on other equipment slots without having to rely on perp gear too much