I did some back of the envelope calculations using our smoke and mirrors learning as a baseline.
- Assumptions: DC to avoid horrible miscast: 30
- Journeyman all start with 15 learning
- Partly learned casting penalty reduced to -15 (college training programme, meaning flat rolls to cast (+15 learning-15 partly learned)
- No penalty for low magic score (3-4 despite needing 7 to cast)
- DC 50 to cast any battle magic spell.
- Pre rooms of oh dear.
Roughly half the class would be rolling on the miscast table. That would mean 15% of those (DC30- learning 15) would run into the dead, warp portal, summon big demons section of the miscast table. That's around a 7.5% (0.5*0.15) casualties.
The not dead failures try again. 42.5% start, 21.25% fail another another 3.18% die. 21.25% try, another 1.5% die. Repeat until you've passed.
That's over 12% journeyman casualties. Per spell. With some fairly generous assumptions and them never having to cast with a lower partially learned penalty again.
There are 8 battle magic spells, many of which are harder than smoke and mirrors. Keep it at around the same scale (casting gets harder but journeymen get better that gives roughly 65% casualties (0.88 to the power of 8 *100) for a fully trained battle wizard. That's with absurdly generous assumptions and forgetting that some people would have to cast with a penalty multiple times.
It also ignores the significant average number of tries it takes for each student to even learn the spell in the first place.