The problem is that there's no "something". All BitTorrent does is make a promise, and that is worth nothing. Thus, "something is better than nothing" doesn't apply.
Now if it were a verifiably half-assed solution, I'd agree with your statement.
They did let iSEC partners review their source code. So, it is not nothing.
But I agree that it would be far more trustable (and popular) if Bittorrent Sync were open source. And there is still a profit model with an open source BTSync: let people (who need it) get a tracker, relay server, and always-on (read-only encrypted) peer subscription.
Now if it were a verifiably half-assed solution, I'd agree with your statement.