My belief is that if you put restrictions on a child's device activity, they will eventually circumvent it, from my experience of having parental controls for some devices I had.

Sure, if they learn how to circumvent their way to unrestricted internet access, they will be able to access pretty much everything, but the word "learn" is key, they will become more literate in the tech they use.

And again, from my experience, the child would pretty much only start trying to circumvent stuff when they become a teen, so it'll work for a while to keep them off explicit content, then you'll probably wanna weigh your options, should I put different parental controls on their devices since they got through it, or should I just let them enjoy their internet freedom?

Edit: so that edit you made, "downvoting it doesn't make it less true", sure, that might be the case, but your comment seems to be getting downvoted since it is pretty defeatist, like nobody should try because it'll be removed at some point. It's just like not wanting to put a cast on a broken arm because "it'll just be taken off anyway.". It doesn't mean it's not useful.