Books and Imperial Deeds are a bottleneck when trying to reach Power Level 30 or Kingdom Level 20. Most of the Books I have it’s because I paid real money for them. There should be a way to get more Books just by playing. Right now, using the soulforge to convert 50 Deeds to Books is too expensive and takes to long. Comparing this to Gold Medals, it can take many battles in Explore because we are usually getting just 2 tokens instead of 3 in Explore level 12, but eventually you can get enough medals to do Elite Gold on many troops and reach the required 20 Elite Gold for a Kingdom. But with Books is impossible, and with Imperial Deeds it can take a long time since we are using many Imperial Deeds to upgrade many things.
Most stuff in the soul forge requires too many resources to bother with. Vault keys are another example. The only stuff I make there are mythic troops when I have the diamonds (rarely), the odd weapon and orbs of power. This is intentional design, as they want people to spend money - however, the costs are prohibitive. I’m just leaving the kingdom upgrades until I happen to have enough stuff for them, eventually, as I’m not inclined to spend unreasonable amounts of money. The “offer” for uprading a mythic troop costs as much as, or marginally less than a game like Baldur’s Gate 3, lmao.