I wrote a blog post in 2015:
Office 365 External Users: Microsoft, Please Improve!
Since then, not much has improved. So much so, that often I advise clients to use BOX, Egnyte, Drop Box, or Google Drive, if they need to share heavily with external users.
To bring the point home, I recently saw an excellent video made by Shane Young from PowerApps911:
Sharing PowerApps with External Users
Although Shane's focus is on Sharing PowerApps, the external sharing components of this video really overlap with SharePoint external sharing and Shane does an excellent job at showing the painful details of sharing content with external people.