Whatever API is being used with your Microsoft partner is causing a diminished experience when collaborating with more than 10-12 users in an Excel spreadsheet compared to Google Sheets. I understand that these platforms are fundamentally different and handle collaboration with their own set of customized tools, but the experience in collaboration for Excel for numerous users should be as smooth as working on SharePoint or OneDrive. We don't allow Google in our workflow, collaboration in Excel is laggy, slow and terrible.