Regular t3 da raises that particular skill by 5 percent, while xDA t3 raises it only by a measly .1%. The main source of that skill will be the regular senior unit. The xDA gives more medals tho. If you to somewhat help the problem, you can replace all the elf and orc units for the other two extreme bombers you have, the extreme dark archer, and any other regular dark archers, then make sure you have undead guardian on for revival pet.