Lots of places on more popular back-country campgrounds now have metal lock boxes. I.e I try now to do 1 trip each year to Robson / Berg Lake and wouldn't even dream taking ursack or container. Problem is when camping wild, specially where trees are scarce. For instance Devon Lakes in Banff NP. Just some boulders, nearest tree couple of kilometers away
I am still tossing whole thing in my head; logic tells me "You need to have both", but besides obvious advantage in terms of size/weight I am not convinced at all in ursack quality. We'll see.