Why not take the front mech across the TT on that Hunter also?
Because that would require either a top-pull FD or a pulley on the back of the seat tube to reverse the cable pull. Some people do one or other of these things, but they add problems which are roughly of the same magnitude as the downtube cable routing, so it's not clear that there is a "best" solution if you want to use full SRAM. There is a top pull Shimano FD-CX70, but I'm not sure whether current Shimano FDs work with other people's levers.
Because that would require either a top-pull FD or a pulley on the back of the seat tube to reverse the cable pull. Some people do one or other of these things, but they add problems which are roughly of the same magnitude as the downtube cable routing, so it's not clear that there is a "best" solution if you want to use full SRAM. There is a top pull Shimano FD-CX70, but I'm not sure whether current Shimano FDs work with other people's levers.