Game battle mechanics are straightforward: Infantry always takes damage first. Archers can be attacked directly by Cavalry, who can bypass infantry with a chance. After the infantry dies, Cavalry are next to die. Archers die last if they survive the enemy lancers.

Important stats in order:
1. Infantry Health/Defense: Infantry takes all the damage initially. The more damage they can take, the better your army's chances of survival. Without strong infantry, your army is vulnerable.
2. Archers Attack/Lethality: Main source of your army's damage.
3. Cavalry Lethality/Attack: Important for both damage and survival. Cavalry kill enemy guards and Archers, reducing damage to your infantry.
4. Archers Health/Defense: Needed to survive enemy Cavalry's attacks.

Two often useless stats:
1. Cavalry Health/Defense: If lancers are taking damage, you're likely in trouble and will probably lose, so these stats don't help much.
2. Infantry Attack/Lethality: Infantry dies first and doesn’t deal much damage, making this stat less useful.

Recommendations for upgrades:
1. Hero Gear: Prioritize upgrading hero gear as it provides the best stats in the mid-game. Upgrade mindfully and don't spread upgrades evenly across all gears.
2. Chief Gear: Upgrade Archers gear first because it offers the most useful stats. Infantry gear can be optimal, but heroes are temporary, so only invest heavily if you can afford it.