In Battle No:1, you had more than 2:1 superiority in men and nearly 2.5:1 superiority in guns (and i suspect you had a lot of Mediums and Heavies in your arsenal).
In Battle No:2 & 3, your enemy was playing "emotionally or desperately" as he attacked with numerical and artillery inferiority and mainly with his 75mm guns for support, in the battle screens i haven't been able to find mediums or heavies (though there maybe a few).
In 1915, Allies do not have the ability to launch huge battles with preponderance of HEAVIES and must rely on 75mms, some mediums, some heavies and lots of numbers. Your opponent ignored this and attacked with numerical & gun inferiority and paid a price against well dug troops supported by some mediums (and maybe a few heavies too).. also your opponent seems short on AMMO and SUPPLIES which have adversely affected his chances.
Despite, all this in Battle No:2 his casualties are alright for a attacker, only in Battle No:3 he seems to have lost BIG.
P.S.: In a historical note (by now you have realised i am a big fan of historical correctness) - the Allied Intelligence (Anglo-American) rated the German 251 divisions post WW1 and gave the 33rd Division (part of the 16th corps) one of the best rankings and gave the 16th corps itself one of the best rankings, being second only to the Alpenkorps (the Best all-round Corps of the War, though its TOE was similar to a division with some reinforcements) and the Prussian Guards and Guards Reserve Corps (the premier break-through Corps of the German Army in all years on all fronts).
Rascals, would you live forever? - Frederick the Great.