I agree that it's certainly not a substitute for a proper security setup, but it definitely makes an attackers life easier - up to the point where it may get in

I agree that it's certainly not a substitute for a proper security setup, but it definitely makes an attackers life easier - up to the point where it may get interesting to automate this. So as always, it's a tradeoff. Both options may be acceptable (and I've run a setup where I'd have internal names exposed on public DNS for years), but you need to be aware of the tradeoff to make that judgement.