So, Hindenburg is overrun and killed by a wisent during one of his frequent hunting trips in Augustów Forest. Subsequently, Ludendorff is sent to the Western Front and given a division.
Mackensen is as good as a figurehead as H. was. He's an unrestrained monarchist, but less popular than H. was. (Beating the Russians in Poland and conquering Serbia is nothing compared to liberating East Prussia, at least in most Germans' perception.) Thus, the Kaiser will be happy.
Seeckt is more of an operator than L. was. (L. was kind of a logistic genius, able to find reinforcements where others found nothing. His operator was Hoffmann.) But his weakness is a certain disdain of logistics.
Seeckt's ability to disregard the politicians is on record. So, he may be as unruly as L. was. But he also may be able to see that the admirals are lying about success in USW. As architect of the victory at Soissons, he is at the root of the realisation that decisive breaktrough in the west is impossible.
Concentration on Eastern Front and OE, no USW, perhaps a quick campaign to push Italy out of the war.