Yeah, this has been always like that, and I also think that selecting multiple details and changing their scale all at once would be the logical thing. I
You can use the detail command after selecting multiple detail views. For instance, if you want 1:4 it would be “_detail _scale _1 _4”
Didn’t know that command, I’ll try as soon as I get in front of my computer. But I think, that what @osuire was asking for should be implemented. It is the expected behavior when working in Rhino with multiple objects when they share some kind of similarity.