Germany was, by far, a bigger threat. Between late 1941 and late 1942, the danger of Soviet Union collapse was very much present. In case SU throws in a towel, that would mean not just relocation of German forces in the ETO and MTO, but also that Germans have access to great amounts of raw material and working population. Germany have had a bigger industrial base than Japan.
All this combined means that beaches of Europe are not defended by few Italian and 2nd hand German divisions and A/C squadrons, but by whole German military, in case SU falls.