2 stability is small in the grand scheme, but as Austria you probably have enough on your plate since PU-ing Hungary/Bohemia, shadow kingdom, and Burgundian inheritance are all things you should be prioritizing. Once you've done those it should be fairly trivial to take and release Byzantium as a vassal if they've been eaten and then return cores next war. Just preventing Byzantium's annexation doesn't massively weaken the Ottomans enough to justify missing out on a PU of Bohemia or something IMO.
In general as a player there's no rush to dismantle other majors powers since you'll be far more efficient than the AI at just blobbing normally and you'll eventually utterly eclipse their power.