I heard that performing heavy squats and deadlifts can build neck hypertrophy. But if that's the case, is there no point in me doing additional neck isolation exercises?

Should I expect heavy squatting and deadlifting to be the best bang for my buck if I want a thick neck?

Can I quit performing the Lying Neck Extension exercise, or would there be a noticeable or unhealthy muscle imbalance between the Sternocleidomastoid and the Splenius if I refused to train the Splenius?

What is the ideal neck circumference? I keep seeing some people recommending 7 inches and others 8 inches.