Full quarantine is effective, almost tautologically so. If the virus is still increasing exponentially then whatever quarantine measures you do have in place simply aren't full enough yet. At the extreme end of a full quarantine, imagine everyone is prohibited from leaving their homes for any reason, and once a week someone in a fully sealed bunny suit comes by to drop off food for the week. That's a pretty darn full quarantine, and you better believe it'd be effective.

Fortunately, we don't need to go to such extreme measures to get the replication rate below 1, but my point is, that extreme measures absolutely do work. The virus isn't magic; it needs to spread through relatively close personal contact. If you eliminate personal contact and sharing of spaces entirely, it cannot spread at all.