> one staffer wrote on an internal EC staff forum that “I don’t understand the added value here

Usability problems aside, I do think the issue of using a messenger that for official government business hosted in a foreign nation is a hard to understand concept and that should be apparent for non-technical staff as well as technical one...

We heard that nations aren't necessarily are sending their best to EU institutions...

Perhaps I am wrong and he complained about the internal tool using its OneDrive integration to host files are something like that.