Just to note, perhaps a little pedantic but the ref targets aren't completely syntactically and semantically redundant—their targets are the sections, while the :class: directive target is the class item, which can make both a syntactic and semantic difference in some contexts. If content outside the class directive, such as an introduction, examples, or other classes/objects is added to the section, then the class directive is not practically equivalent, especially so in practice if the content is added above the linked class, or in a different scope.

In this case, the only current examples of this are a versionadded directive above the Blob class, and some rather lengthy examples below the Row class (which besides being a little lengthy for the context, are somewhat confusing, since it references "the example given above", but is unclear which of the many examples this is—evidently the one in the document introduction). However, additional such material could be added at any point in the future, in which case the refs should presumably be re-added.

Whether they are worthwhile to keep, though, is up to you.

Some other more minor notes:

• If the class is ever renamed/replaced by another in the same section, class refs will break, wheres section refs will not. That's pretty unlikely, though.
• While no internal links may be using it, it is theoretically possible that external links might, if there was a previous :ref: and they copied the link from that ref, (or manually did so, for a more robust link than relying on the section name not to change). But again, that's pretty unlikely.