Арена Tactician's Corner

with the support of strong units (like archers and cruisers) from another castle, you can certainly create a powerful combination.

Let's analyze. (You also have archers and cruisers, so you realized that someone would be stronger).
So, the support is equal. And 15,000 HP survived, which means that those who are supported are stronger than those you have. That is, skeletons, vampires, dragons, etc.