Depends.
Isolation exercises are better than compound exercises for inducing growth of the target muscle. For instance, a cable cross-over is better than a bench press for the chest.
But, because of things like neuroendicrinology, and the actual ROM that each movement has (the point in the lift where the muscle is contracting with the most forcee), the efficiency, among other things that compound lifts cause make them superior overall.
So, if you need to gain 20lbs of muscle, focus on compound lifts and eat. If you need to bring up your chest in specific, do your flyes and limit compound work for that part.
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Complex problems have simple, easy to understand, wrong answers.