The web versions of MS Office tools are actually pretty well build and feel pretty close to their desktop counterparts.
If you have to write papers with a lot of math in them libreoffice's equation editor is way better anyway. It rarely crashes and uses it's own simple markup language instead of the finicky WYSIWYG editor in word.
1. Word - track changes 2. PowerPoint - equation editor
As for the formatting - yeah, MS doesn't seem to follow its own document formatting standards, even for the newer documents. That puts other suites in a hard spot: a) follow standards and present imperfect documents, or b) invest immense resources into bug-for-bug compatibility?
I don't know Excel but I know there are people running entire departments on Excel spreadsheets.
(Having seen many Excel spreadsheets, 80% of the work is done by rudimentary means: pivot tables are Advanced Magic in this regard)
You can edit the markdown in vim which IMO is mentally easier to write prose in because you're not distracted with all the formatting and spelling. You use aspell for spell check and pandoc/pdflatex for typsetting.
It should be able to handle most use cases