Two problems are to be though about:

Dodecannese islands are needed to attack Ploesti (fighter forward base) and you can't let the Germans and Italians just happy in Greece if you want to hold these Islands.

If Peloponnesus could have been won during the first landing, it could have been a good place to buid large airfields to attack Italy from South-East (different axis than from Algiers and Tunis).

Jacques