Outlook, Outlook Calendar, Teams, SharePoint... I'm honestly baffled by how bad they are. It's like it was made by aliens who only sort of understand what human beings want. And, of course, Microsoft is super selective about their product managers and pays them a ton of money--even though a golden retriever could have come up with a better UX. Literally all they had to do was fucking copy Google.
You are correct, SharePoint is the backend to teams. SharePoint requires more setup for users to actual begin using it. OneDrive is just a place to put things, less work than SharePoint but less feature rich