You’re forgetting that at the first kage summit the tailed beasts were evenly split, each nation got two except for Hokage who only took the 9 tails. Why would he only take one tailed beast u less it was the most powerful one.
Theory: it’s the tail number plus the previous tail numbers (I believe they call this a factorial in math it correct me if I’m wrong) so:
Ten tails=55
Nine tails=45
Eight tails=36
Seven tails=28
Six tails=21
Five tails=15
Four tails=10
Three tails=6
Two=3
One=.....1(duh)
so as u can see the...