Edit: maybe Im misunderstanding you, are you talking about cards SLOTS? Other can have card slots, but we dont need all these filled, right? At this point, not adding cards to the elements cannot be justified by lack of card slots. If the space is even going to be completely filled (like 20 years from now), something else can be done, like remove useless cards, reedit them, add more space.
I also dont feel that these shard effects are generic. The small effect related to an element can be generic. But we are adding a bigger effect that is not, or at least was not generic until now. Draw acceleration, for example, was not a generic effect.