Mages – their development.

400 gargoyles and 50 djinns, but I figured there was no point in using them.

But that was a mistake! Gargoyles are armored... Djinns are a great offensive unit... Big mistake...

Paladins with a bonus destroy everyone.

And that's where gargoyles would have been useful - just stand in front of the paladins and block them, preventing them from using their ability to spread out.
Next... I didn't see any mention of mini-arts... Were there any at all?...
What was the hero's level? At least magic...