In v16.3, (PR #20042), you’ll be able to disable the Tiptap capabilities in the RTE data-type config, e.g. remove “class” and “style” attributes. But this would mean that some of the other extensions like Text Color, Font Size, etc wouldn’t work.
With the <o:p> tags, from what I’ve tested, the o namespace prefix should get stripped out, leaving only the <p> tags, but this may depend on the document’s content being pasted in. 
I like @huwred’s suggestion with the dedicated extension, that looks to handle all the MS Office markup scenarios.