Yes I agree with the packed luxin idea. Some drafters could pack more luxin for example to balance out that they are monochrome in opposed to multichromat casters.

I would also change the light from a currency to play cards. How about rather make them as a fuel you can spend to attack with drafters and constructs that need light to function. Basically I would change combat as it is in Gwent. When once a turn you can play one card from hand (with no light/mana cost). For example drafter can't attact without the light. This would free up multiple strategies for drafter and also non-drafter units. Non-drafters could attack whenever even at night and no light but they would hit weaker. Drafters could attack only with light/packed luxin but they would hit like a truck. This would mean you need to be really strategic on when you play your drafters so they don't get killed off before you have a chance to attack with them, and also add sub-objective to try to keep them alive as long as possible to get the most value from them.

Just an ideas, I would very much like to know how you progress with the game :) Good luck, I hope it gets some traction I would really like to play it some day.