Well, in fact it is there already. In 1914, the British corps of the BEf are rated 8-9-4, whereas the best French and German are 6-7-4 (and only one 7-8-4 for the ultra elite)... so British firepower and excellent marksmanship is already represented in the game.
The +0 to +3 value termed firepower bonus you see on some units (in the yellow circle) is in fact representing the corps' intrinsic Artillery firepower...and in that matter the British were on par (or even lower) than the French or Germans.
By 1915, the 'quality' of the professional BEF had vanished (due to losses plus the fact that the experienced NCOs were versed into new corps as cadre), so the top-quality 8-9-4 corps are removed and replaced by 'standard' 6-7-4
