Also DERP relays having QOS that isn't controlled by myself and I have to hope to get bandwidth through doesn't exactly make me confident about the solution
As for your bandwidth concerns in the case of needing to relay, you can even set up your own relay (https://tailscale.com/kb/1118/custom-derp-servers), which would satisfy your desire to be more centralised (i guess you could force all traffic through it, but cant think why you would want to) while still allowing the flexibility of the overlay that tailscale provides.