Yes,
a) I am currently duplicating all files, from Pool A to Pool B. But I still need the Hierarchical pooling to do so because Pool A has drives 1, 2 and 3 and Pool B has drives 4 and 5 which are the designated duplication drives. I cannot do that with just one flat pool with drives 1-5 because I cannot force drives 4 and 5 to be the only drives where duplicates can reside. (e.g. I don't want files in drive 1 to have its duplicate in drive 2 or 3). In reality, Pool A has local HDDs 1, 2 and 3 and Pool B has cloud drives 4 and 5 so I want to make sure that the files in the local HDDs are being duplicated to the cloud drives, not to another local HDD.
b) I am backing up Pool X (full duplication of Pools A and B ) to "Backup A"
c) I can but that adds more pools. In the above Hierarchical pooling, I can have unduplicated files in Pool A (in drives 1, 2, and 3), that doesn't get duplicated to Pool B (drives 4 and 5). I can keep growing Pool A to host all unduplicated files while growing Pool B with just enough storage for all duplicated files.