Structure (buoys, bird racks, rock piles, etc) are more critical than chumming.
Crazy patience is what I'd list as the second most important "skill" needed to catch them reliably, at least if you dedicate days to specifically targeting them vs. simply putting a float with a pin out the back when drifting (which WILL eventually work but with sharks and other fish added in the mix). I dedicate full days to it and on good days with double digit cobe hook-ups don't regret it an iota. On days with no bites (rare, but does happen) or bites spaced about 3 hours apart I sorely miss drift fishing for trout, reds, macks, and the more constant action it provides.
Chumming be about 3rd or 4th on the list of what I've used to catch them. Typically I won't put out any chum until AFTER I've fished a few hours and the bite proves to be off. Probably caught 80%+ cobes without it and under 20% while using it. Not that chum doesn't work. It does. But in addition to cobes it's going to bring in other fish as well, such as toothy macks and sharks that can make for lots of cut line and re-rigging. Sometimes the sharks are a good thing as they'll have a few cobes with them, but often the sharks will be alone and prove a nuisance. Sharks take the chum bag too if I'm not super careful to make it tough to grab and keep a watchful eye on it.
Long answer to your question, but guess the short answer is -- just depends.

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