One of the biggest problems with Splinterlands is that lower-level play is nowhere near as challenging and fun as higher level play.

The solution to that is multi leagues. A novice league that only allows novice cards to be played in it.

I don't see how your suggestion is a card sink. To me it looks like just the opposite. Its likely many players will opt in to having a level 8 max card that only cost 10 combined cards vs. needing to combine hundreds which means more cards left in the market for sale.