I mean even then, I prefer the opposite route: Remove the CD rather than the cost. We can already only produce cartridges at a certain speed, so things could as well have been reworked to remove the time-based restriction instead of the cart-based one. Bonus points if the skill automatically gains potency over time, but otherwise has no CD, meaning we could press it ~whenever, but the potency/cart only maxes out 120s after last use.