As a daily LibreOffice user, I agree with you on the UI. I can't even keep track of how many different settings menus there are and each of them are a labyrinth unto themselves. What ended up saving my sanity was setting the UI to single toolbar and purging every unnecessary button in Calc and Writer. Might be unpopular, but I then arranged the remaining toolbar features the way they do in Google Docs. For Impress, I set it to the tabbed ribbon-esque interface.