In the Win3.x and Win9x and NT4 days I built and maintained computers labs at a community college.
For Win3.x, WP5.x and 6.x shipped with a msvrt.dll and one other MS provided DLL that was identical binary (and version number) to what was shipped with Windows itself. The WordPerfect installer replaced the Windows installed copy with it's own copy where the timestamp was the only difference.
As soon as you installed MS-Office these two DLLs (in the windows directory) were replaced with different binaries which reported the same version number.
Once installed, WordPerfect would be slower and more crash prone.
I don't know if this was a planned/malicious change on the part of Microsoft or just crappy version control development, you decide.