As we know, Shiryu is the #2 of the BBP
But why exactly is this the case, when Kuzan is objectively stronger? Let’s drop the cap and agenda for a moment. Kuzan utterly shits on Shiryu in terms of feats and portrayal.
The only thing shiryu has over Kuzan is #2 status, but that doesn’t necessarily equal strength.
The real question we need to ask is, why is Shiryu #2?
I think it’s because the two are related. I think Shiryu shares Teach’s special lineage. I would guess it’s something like Orochi and Kanjuro, where they are part of the same tribe, but orochi/Teach is the descendant of someone important.
Anyways, because they share lineage, I think Shiryu’s goals align the most with Teach’s and hence he is Teach’s most trusted subordinate.