An XML format, even one with a lot of cruft to handle legacy complexity, is absolutely easier to parse/interop with than a legacy binary format that was to a large degree a serialization of undocumented in-memory content.
OOXML was, if anything, an attempt to get ahead of requirements to have a documented interoperable format. I believe it was a consequence of legal settlements with the US or EU but am too tired at the moment to look up sources proving that.
> is absolutely easier to parse/interop with than a legacy binary format
depends
you can have well, clean and fully documented binary formats which are relatively easy to parse (e.g. msgpack, cbor, bson)
you might still not know what the parsed things mean, but that also applies to text formats (including random documented binary blob fields, thanks to base64 they also fit into any text format)
OOXML was, if anything, an attempt to get ahead of requirements to have a documented interoperable format. I believe it was a consequence of legal settlements with the US or EU but am too tired at the moment to look up sources proving that.