"And I could represent the same data in a second hierarchy"

Thank you for making my point.  In order to represent data stored in a hierarchical structure, in a different hierarchy, redundancy is required.

Data stored in relational structures can be represented in many different hierarchies.  It is much more difficult, if not impossible, to do with data stored in hierarchical structures.  Granted, representing complex hierarchies is...well...complex, unless you store it that way.  But in so doing you limit the data's usability for other purposes, and you loose the ability to declare any but the most rudimentary constraints on it.

So, now you've flushed data independence and data integrity down the drain...  Let me think... What was the purpose of a DBMS in the first place?...

If you need any further proof that hierarchical structures are very poor for general data management, just look at all the problems with file systems.  The organization of file systems is notoriously difficult because what makes sense for one person or group, makes no sense for others.  So what happens?  Multiple file structures are created to support the different useful views of the data.  Then files are duplicated all over the place, many are fogotten and very quickly, no one has any idea which files are current etc...

Hierarchical data management is a mess.  Those who are smart would avoid it.