FYI: The reason microsoft uses Word to render html in outlook is very simple: In the earlier days, IE was used. So everything worked perfectly well. But then came along politicians (EU) who prohibited this. The reason IE is not allowed to be used as rendering engine in Outlook is that IE is delivered as part of Windows and not as part of Office. And Outlook is part of office.
It’s the same reason we now have Windows versions without Windows Media player (atleast in the EU).