Earlier quoted context omitted.
"The only downside is that there is no good iOS app." That's a dealbreaker for iOS folks, though. I hate the mission creep Dropbox has embraced, and would definitely consider something else, but I need access to my stuff on Windows, MacOS, and iOS. Anything that doesn't hit all three notes isn't a contender.
To me it's a dealbreaker for iOS. iPhones are just toys that don't get real work done. I take a photo with with my phone and it's synced to my Linux desktop in 1-2 seconds.
Working with the filesystem was very tricky in the past but this is no longer the case with https://developer.apple.com/documentation/fileprovider for the past 4-5 years.