Scripts

So, it becomes interesting, which of these will be less demanding on the map? What should be prioritized for script optimization?

If the developers aren't incompetent (and they aren't), then it should be done through a trigger. Because a trigger that's not active doesn't execute until the corresponding event is called. But a loop constantly executes, which puts more load on the map.
In your script, in

GetSavedCombatArmyCreatureInfo( combatIndex );

you only passed 1 argument, but you also need to specify 0 as the second parameter (0 for the losing side, 1 for the winning side), and the third argument should be the index of the army slot to check. Accordingly, it's better to write a loop that checks all slots.
That's why it's not working. The manual doesn't explain it very well, but as Khottabych already pointed out, it was discussed on the forum.