Barrel made much before WWI were generally made of iron, and not steel. So, yes, relatively speaking, the metallurgy was poor, compared to what can be done today.
Its very difficult to find an original( authentic, as you say) firearm in good enough condition to shoot, that should not be left in a museum. The benefit of shooting replicas is that the originals can be around for 100s of years for people to study, and understand, hold, and admire. Replicas offer a gun made of modern materials, at a cost far less than what you might have to pay for an original.
If you can find a fowler in original condition, that is in good enough shape to shoot, its value would be in the thousands of dollars- far more money than most people could afford to risk damaging or losing. Why not just get a modern replica fowler and shoot that?