Random is crap; a lot of the time you will only win because the CPU can play stupidly. Most of the time, your cards just will not be able to stand up to the NPC's stacked deck otherwise.

This isn't the problem. I got this alot against Indolent Imperial and Vorsaile, where 10>11. I'm dropping a 6+5 Frixio on an 8+2 Nero or a 9+1 Bahamut and... nothing. Nothing happens. Why, cause 10>11 apparently.
Nope, but 10=10, and no matter how high a card ascends it won't go over 10. The game explicitly tells you this, so it's not an oversight.