PC Version:
To upgrade a kingdom from power level 21 to 22, I need to unlock 31 traits on troops, collect 2 mythic troops (already fulfilled) and upgrade 5 troops to elite level bronze.
In the second offer of daily deals, that is there to offer power upgrade materials, I am given the option to purchase kingdom troops of common or rare rarity, explicitely as a way to increase the power level. This has happened more than once.
I assume, it is the medal requirement, that is confusing the game in here. Please have a look into this.