While good in theory, it wouldnt actually work. I once battered down nearly every section of wall in Rome, (as the Seleucids) yet whenever I went to besiege the city I had to build siege equipment. So even though the wall was unrepaired and there were openings enough for three full stack armies to comfortable march through, you will still have to wait in order to attack a settlement that has walls of any type, in any condition.