I sense your argument might not be with the people here, who are merely trying to help you with practical advice, but with the UK government (and the Scottish administration under devolved powers)
. None of us are responsible for what might appear to be conflicting and illogical policies!
FWIW, I think you're approaching this sensibly and I hope I'd do the same. I would personally wait for what comes out of today's announcement because it might well be that it makes the situation an awful lot better for you.
Failing that, every indication is that in 3-6 weeks after the start date the quarantine will be dropped for arrivals from most countries. I'd certainly expect Germany to be amongst them. That leaves you free to decide which of Germany and Scotland is going to allow you the greatest amount of freedom, as you identify.