I'm convinced that barring kids who are exclusively homeschooled, every kid has a way to bypass these restrictions either by themselves or with a classmates help.
That’s true of nearly everything though. That lock on your front door? I can easily bypass it but yet you still have it. Anyone determined enough can do almost anything. But throw a wide enough net and at least you can prevent the casual and lazy offenders. Also I think prevention is an ongoing thing not a one and done thing. You shouldn’t say “oh I put a dns block on YouTube so now I don’t need to follow up on my kids” and I feel a lot of parents do just that.
