We can get rid of the extra XHTML pre element by noticing that it always contains an XHTML b element child.

This step can remove that element:

<p:subtree select="h:pre">
  <p:route>
    <p:when test="h:pre/h:b">
       <p:delete/>
    </p:when>
  </p:route>
</p:subtree>

This deletes a 'pre' element when it contains a 'b' element.