Appears to be the fungus entomosporium, not anthracnose. The latter is a 'catch-all' term used by those who know just enough to get themselves into trouble. Mountain Ash happen to be quite susceptible to this disease. The fact that they have been through some serious stress compounds their inability with withstand disease and insect attack.

One spray will never 'cure' them. These fungal spores are ubiquitous....and your plant is prone to infection. That makes control a challenge, especially once the disease has expressed itself.

When the leaves fall this autumn, be sure to rake up and remove them from the area. Put them to the curb for pickup, don't use them for mulch or compost. Avoid excess fertilization or pruning practices that may stimulate lots of new growth. There are fungicides on the market that can help you control the disease and they are readily available. I never make chemical recommendations in the GardenWeb, but I know that with a little bit of research you can come up with what you need to know.

Peeling bark would certainly worry me. Perhaps you could link some images of the trunk, fairly close up as well as from enough distance to see normal bark tissue, as well. The fact that the flowers appear to be perfectly healthy is of little or no significance. In the future....FYI.....smaller plants establish much more easily than larger ones.