No, it most certainly is not.
You would be very hard pressed (pun intended) to find someone above the intermediate level who trains for size and doesn't do some degree of isolation work, which should always be done for many sets of high reps imo to prevent overstressing already weary joints and tendons.
Flyes I don't personally do (beyond the DC extreme stretch for chest), but rear delt work, biceps, calves, abs, hams, laterals, pushdowns all have a place. Not to mention all kinds of pre-rehab work for adductors, hips, glutes which you have to do if you don't want to crumble under a heavy workload.
I would venture to say that most people doing the basic 'squat three times a week' are probably not lifting enough to grind them down if they tried to train on compound only.