Christopher - yeah, most of those other things don't bother me (much - placing Arthur anywhere but the 6th century is just wrong!). Maybe I just have a been in my bonnet over Holmes. I love the Brett series SO much, it's become the defining Holmes for me.
Although it's perhaps worth remembering that the Holmes stories weren't period pieces when they were originally written, and that, of course, Basil Rathbone was doing Holmes in the present-day as far back as the forties . . . .