You can probably still have a meaningful bpf sandbox even without the setuid root helper (or user namespaces), but I'm not sure Chrome supports running that way (because it doesn't make much sense from a security tradeoff point of view). As ugly as it is, the odds of a bug in the setuid helper are probably smaller than the odds of a bug in the attack surface its mitigations remove.

But the setuid helper and user namespaces are used for other mitigations that can't be done through bpf. The guys who wrote the bpf sandbox have some nice articles about the distinction which you can probably Google.