That's down around 170k (less than 2%) for Strictly on the final last year, which I'd say is a pretty negligible drop. Plus it had a 59.8% audience share. Given that it seems to have been as well received as any series recently, I think the BBC will be more than pleased with how it played out this year, given the bad headlines it was getting for most of last year before the series started.
I think I made a mistake for the last week when I referred to Masterchef, when I thought it was the final week. This week (which I believe WAS the final week), all three shows charted.