By 1900, there were relatively robust systems in place. The 1890's saw a real burst of creativity and understanding. The Boss single trigger seems to have set the pace. I am under the impression that there are shooters for whom double triggers really are a detrement. Considering the social pressure that surrounded the upper end of shooting, some were willing to pay serious money to solve the single trigger issue. Boss got that job done. Others followed.

Personally, I rarely remember moving my finger from trigger to trigger - it just happens on auto-pilot. On the other hand, I don't suppose that because it works so for me means that it should be so for everyone.