Syncthing replaces the syncing, not the cloud drive. Files move directly between your own machines, encrypted in transit, with no server in the middle holding a copy. If what you wanted was a backup, this is not it.
What you are replacing
Dropbox gives you two things that get bundled together in people's heads: continuous sync between devices, and a copy in someone else's data centre. Understanding which of the two you rely on decides whether this migration works.
Peer to peer sync between your own devices, with no account, no quota and no third party storing the files. For a laptop, a desktop and a home server holding the same working directory, it does the job better than a cloud round trip does.
What it does not replace
There is no server, which means there is no copy when every device you own is in the same flooded room. Sync is not backup, and treating it as backup is the way this choice ends badly. Sharing with someone outside your device set is also far clumsier.