It still works well in the appropriate settings. LibreOffice (nee OpenOffice) uses ODF, an XML format, for its document files, and it has been working nicely enough for a long time.

MS Office's own XSLX and DOCX formats are trees of XML files, zipped.

If-I-Recall-Correctly, it was typically a 10x memory load to open an XML file in a DOM parser. Which could get really ugly, really fast when you were dealing with many files.