> You've no guarantees that your local'ish data centre is going to be hop-wise, route-wise and peering-wise any better than a DC 1500 miles away, in relation to your home or office ISP.

You're correct. In fact, as I type this reply my cloudflare diagnostics are indicating I am talking to a datacenter 200 miles further away than would otherwise be ideal. That said, its still within an extremely reasonable distance. This is a "risk" I am willing to take. It's certainly a better starting point than guaranteed 70ms minimums.