There's no way in hell you know if any single incompatibility is caused by Microsoft not following a standard.
If a file is created under a Libre Office and opens fine under WPS Office but does not open fine under Microsoft Office, which I can assure you does happen, than Microsoft Office is the package with the compatibility issue.
The number of pages is irrelevant to the consumer, but standards should be bible to software developers. Problem is Microsoft believe they're above standards and that's no accident. Docx and xslx are both standards, compatibility issues should not exist between office suites at all.