In my opinion, they do different things.
SFTP/SCP are great ways of transferring files between computers. I prefer rsync for most things because it can resume transfers and checksum results. I'd never use FTPS because SFTP/SCP comes with SSH, and why run a separate service? SSHFS is another way to use SSH to transfer files (it mounts a remote file system to your local computer so you can use all your normal file management tools).
NextCloud (and similar) do a bunch of additional things:
- Provides clients which sync files to your local computer
- Provides a web interface for managing files
- Provides ways to share files without creating accounts
- Allows connecting external storage (eg. S3)
- Provides encryption
- And a lot more
If SFTP does everything you need, that's awesome. Use it. :-)