The Orchos Rabbeinu may have been arguing on the rabbis of the Kibbutz HaDati movement who expressly permitted trousers. Both opinions have legs on which to stand. (Sorry for the pun.) Who are any of use to argue with either? In the spirit of Yom Kippur, lets allow each of us to follow our own rabbonim and cease charging others with not being frum. On this day of all days we should be looking at our own sins rather than at others.
Gmar Chatima Tovah!