Since nobody has answered the OP's question, I'll answer it. It's the trimming. Trimming is the biggest annoyance in riding a mechanical shifting bike. Especially bad when you get to the wider cassettes like the 11 and 12 speed cassettes.
To be fair, SRAM did conquer this problem with the Yaw technology which changes the angle of the FD slightly in each chain ring.
To be extra fair, Shimano also conquered this problem back when they made the RSX brifters with no trim function- the narrow 7 speed cassette didn't need trimming in most instances (You just have to avoid big-big IIRC)
To be extra, extra fair, Suntour also conquered this problem even earlier back when they introduced the 'Symmetry' top mount shifters. As you (friction) shift the rear shifter, the shifter mount will move the pivot for the front shifter, and adjust the FD slightly to compensate.