I think it would be useful to be able to generate deck suggestions based on the most successful decks (decks used by the top players) and the player’s card levels. Here is a suggestion after trying to implement this myself (and failing due to hitting the API rate limit):
Rank decks based on the sum of the differences in card levels for the deck (i.e., sum(max card level - current card level)), where the closer to 0 the more relevant the deck is.
If you do end up working on this feature, I would love to hear how you could optimize to work around rate limits!