Maybe a color coded card system would make it easier to new and familiar players to know how to build decks
With all the water under the bridge, we’ve come to understand the cards can be cathegorized in the following types:
Economic: Villagers, resource crates, gathering rate upgrades, resource trickle or swap.
Military: Unit call ins, unit upgrades and mercs
Modifiers: cards that adds new characteristics to units or buildings. Ex: Blockhouse Canons (adds falcs and mortars to the blockhouse), Palatine settlements (german houses grant more population), early skirmishers (french skirms available at colonial) or Tirailleurs (turns xbows into skirmishers).
Just like in TCGs, you could relate a colour to each type and work with the familiarity to make the deck mechanic easier to understand.
Economic cards could be yellow, military cards could be red, modiffiers could be white.
There are some card that are a mix of two of these types and there is also some considerations to have, like with water cards. Water cards come in the shape of the other card archetypes, but it would be missleading not to signal players that these cards are only usable on water maps. This is easilty solved by using two colors like the game already does with TEAM Hessian Jaggers having both the green team colour and the purple unlimited colour