xiAo-Shin Star the battle was actually really close, two pretty similarly powerful armies. Their strategy worked better against yours, giving them an additional boost. Your skeletons got wiped in long range, so they basically served no function other than absorbing a small amount of long range damages - I wonder if your racial strategy would have been a big help here because that loss was 1/3 of your melee attack power removed from battle before it could do any good.
Short Range wasn't really noteworthy, you lost the rest of your TC and a small chunk of ATC, the defender lost a pretty even mix of all units. In Melee is where the big battle happened with both sides pushing out pretty huge attacks - you around 60k and them around 90k, which was able to zero out the rest of your surviving units (mostly ATC), and it's where you did the most damage on their army. In total you wiped out 75% of their force, while getting fully zeroed out yourself.
Besides them using the right strat in this battle, they also beat you on military tech (by a LOT). Ultimately it didn't really matter what strat you picked, I think you would have lost in any circumstance in this battle. Even if all your skeletons made it to Melee the best case scenario would have been that you zero out their army so both sides had 100% casualties, which would have still given the technical win to the defender... The only way you really could have won is if you had a lot more long range units to help take them down before their huge short/melee attacks could happen. You did have a lot more attack power than them, but they had more defense power, and their long/short attacks were much more devastating against your weaker-defense units.
I think Undead could use a UWDA adjustment like I've been doing for Gnomes though, trying to improve our fodder survivability. I reduced UWDA for Undead to reduce skeletons from 3 to 1.5, pikemen from 3 to 2, archer from 3 to 2. If skeletons still can't get through long range then maybe we can try bumping them down to 1 to see if it helps.