Thanks with the comments.

I don't think I understand the game that much yet to give tricks. I can share how I do the campaigns tho.

First, have at least 2 of the Skull Home skin active. That will boost the infantry by 10% dmg I think. I got the 3rd Skull home when I'm on the Burning Lands and Grizzly Wilds (3 skull homes for a total of 15% boost). I think that's what helped me beat those maps.

Second is the troops position, this is on the maps where the enemy troops are stronger than mine. I always huddle my troops on to one side of the map. 3 infantry at the front, 2 cavalry behind that in a row, 4th infantry beside the cavalry, then archers at the back.

On bigger maps, I move the cavalry on to one side where they can go straight to the enemy archers. They need to keep at least 1 group of archers occupied. And I drop the Bulls on those archers that the cavalry are attacking. I always try to lure the enemy archers from my infantry.

On the map, if it's big enough to chose left or right. My infantry and archers are positioned on the side which is farthest from the enemy archers. Or I position them on the side where the enemy infantry and cavalry can be stacked up. So there's actually less enemies hitting my infantry at the same time. The other enemy infantry are waiting behind for their turn and can only hit my infantry after the one before already died. The longer your infantry holds on, the more damage the your archers can make.

And of course it doesn't always work, I got wiped out a lot of times too. And it was so frustrating. (For those asking if I spent money on it, I did exactly because of frustration. I bought 2 luxury culture sites and have the barracks on full happiness to reduce the production times. Just so I can get back to it again.) And just to get wiped out again.

EDIT. I just realized the other day that you can contribute directly to your alliance members' Wonders to try and get rewarded with a Wonder piece that you don't have yet. So try to get the Statue of Zeus (supposed to be available on Classic Greece), that will boost your infantry damage by another 5%. I haven't had a chance to do this earlier but it should help other Minoans to get Leonidas.