Yes indeed, you are right Tinstaafl...now.
But in days gone past, that third attitude indicator was not available, and certainly was NOT when I received my command rating in the B707 years ago, at least on the Boeing aircraft that I operated.
Far too many now fail to realise that the "comforts" they have today are at the expense of those that have gone before.
Ah yes, switch to alternate (or more) sources, but in yesteryear, few and far between.
I wonder how many remember the canyon approach (otherwise known as, rapid descent and pull-up) required for the FAA ATPL, with the primary attitude indicator failed mid-maneuver?