Super Debuff Move Questions

[Amaterasu]

0 is just the "below average" rank. I don't see why you couldn't drop a stat that low, considering you can start with 0s in up to two stats.

But this is also something to consider. Weakening his opponents is more in line with Usopp than powering himself up anyway.

The step from 10 to 7 stat points is much greater than the step from 10 to 13 stats though, percentually speaking. And the impact of it is likely to be larger.

One thing that I cannot promise would be approvable could be that Usopp uses some sort of long-lasting debuff that makes it seem like he is more powerful, when in actuality his opponents are slightly weaker, though it's still translated as Usopp gaining stats?
(so for instance he has higher DEF, but it's explained by that the debuff makes his opponents' attacks weaker)