I guess it all depends on yardage. Myself, shots with my 45/70 are all within 75 yrds, and usually most all the time in the bush. I can hit a running deer much more easily with my open sights than I can with a scope at those short distances. With practice these little guns become an extension of your arm and you just point and shoot without need of a scope.
Those who shoot a longer distance, for sure a scoped rifle is best, but in those cases I prefere to use a bolt action in those long distance circumstances.
I prefer a lever for its speed in the bush, and a bolt when hunting where longer shots are going to happen.