The only way to make the best card is either using combining cards or farm from the latest monster with best stats. sadly those latest card has no level restriction for master level.
with this system, the old cards will be forgotten and has no use for anything, even when the card itself was combined/refined.
I have some ideas that might be worth to think about the latest card system, which is
1. Give Penalty to some cards so that card won't be the only one to use.
2. Update the card combine features.
3. New Skill Card Features
1. Updated Card : - Giving more move speed with decreased stats for doing long range quests.
- Giving more drop rate/decreasing durability consumption so it will take more time to repair stuff with penalty on some stats.
2. Card Craft : 5x A cards + 2x B Cards + 1x C Cards + Some Monster Drop Materials = New D card with matching stats for the current level
3. Some cards can enhance a specific skill, for example a basic provoke from knight will only give debuff provoked to monster, with enhanced cards the provoke skill will give more effect like slow, poison, or etc as long as it don't break the build for the class.
by giving the card some penalty in stats that means the player will have more to think about which card should be equipped, giving more probability for the stat and skill tree.
by using updated card crafting system, old cards will also be treated equally with the latest cards
by using skill card, it also giving the game a new features to be explored (the idea is like greenseed runes but for cards with specific class and skills)
thanks for reading