I've read most, if not all the books written as first person accounts by people who went through the training system during WW1. The consistent theme is that prior to 1917 and Major Smith Barry's influence on instructor training, the carnage in training was horrific. This was down to poor instruction by people who weren't interested and had little understanding themselves of basic principles of flight, combined with pressure to cut training hours. Unreliable engines and rotary engines with their peculiar handling traits (rich cuts after takeoff for instance) and one sided torque characteristics such that in the Camel, right hand turns needed full left rudder if a spin was to be avoided.
After Major Smith Barry, things improved but not enough to alter the statistics for the whole war.
It must be remembered that even in WW2 the training losses were pretty bad as well.