If their situation is not worse, why does Germany capitulate sooner?
It might not Germany's particular situation; i.e. it could be that Turkey and Austria have collapsed, and Germany sees they can't fight on alone. But that would also relieve strain on Russia.
I just don't see how Germany would capitulate a year early without other major changes first, barring some kind of ASB event like a meteor destroying Berlin. Or an American inventor developing a really effective tank, and the US Army shows up in 1917 with an armored corps that blows right through the Western Front, so that from effective PoD to German capitulation is only a few weeks.