Ugh the misinformation in this thread.
Wide profile cantis are optimized for pad-to-rim clearance, NOT braking leverage. A low-profile canti with a low straddle cable can give excellent braking performance, even compared with V brakes.
Interrupter brakes are great, if they are installed and used correctly. Many riders stay glued to their hoods, however, and therefore think they serve no purpose.
It looks as though it's a used bike? Perhaps the shifter cables need a little TLC. The shifters themselves, all they can do is pull or release cable.