ATL For Market Garden to fully achieve its objectives, they would need to clear the naval approaches to Antwerp starting the last week of August 1944.
OTL When the exhausted Canadians captured Antwerp, they needed a week or two of rest before they could resume the advance.
ATL Even advancing the few more miles NW would have cut off the narrow Causeway connecting Walcheren to the mainland, hindering German supplies.
OTL During those weeks, Germans reinforced Walchern Island.
ATL WALLIED paratroopers could have contributed more if some were dropped on Walchern.
ATL if Market Garden succeeded in crossing the Rhine in September, they could have avoided much of the winter flooding of the Lower Rhine. If Bradley and Patton had not wasted so much time in Hertgen Forest and capturing Metz, they could have turned northwards and helped "bounce the Rhine" at several more places, actually getting significant numbers of WALLIED troops into Germany before winter.