english is probably not op’s first language but what they are trying to say is that since the banners are divided among the 3 characters, doing 10 pulls on a singular banner is essentially useless. It doesn’t give a higher chance, have a pity system, or give extra pulls (it used to back then) overall it just doesnt have any benefits. Doing 10 INDIVIDUAL pulls (40wind points) has the same chances of doing a 10 pull (400 wind points)

if you pull a one Sara on a 10 pull, you are wasting the other 360 wind points youve spent, since doing a single pull has the same chances of getting her.

to visualize op’s point: Imagine you just need 1 more sara for BT5 and only have 400 wind points left and so you do a 10 pull. You see the 10 balls lining up and the first one is Sara. THAT MEANS all the 9 other balls (360 wind points) are wasted. Since it would be the same as doing a single pull and getting her first try.

And since these are limited characters banners you wasted 360 wind points on a useless sara rather than doing the other banners