IMHO, it wasn´t Wehrmact ´doctrine´ to use the Panzer formations for both creating the breaktrough and for the later exploitation phase.
The difficulties of the late-war Wehrmacht on the offensive was caused more by the decline of the quality and manpower of the infantry divisions in the later stages of the war and the comparative lack of air/artillery support. No German offensive from Zitadelle onward looked good on paper even before they started.
During both of Germanys last offensives on the western front (Battle of the Bulge and Operation Nordwind), the task of creating the initial breakthrough was placed on the Volkgrenadier Divisions.
When the understrenght and badly trained infantry formations failed to achieve their tasks, the PzDiv reserves where either called upon to create the breaktrough themselves (12th SS hammering itself bloody on Elseborn ridge during the Bulge) or the offensive called off (Nordwind).