That exactly what I'm NOT saying. I'm saying that a mono/duo/trio deck will have almost no chance to bring down the shield from 90-100 percent, because it has to pay !8 times! the quanta you pay.
The obvious alternative would be to decrease the cost of low tides. But that would make the card close to worthless against rainbows, hence I said that I don't see it as the way to go.
Keeping the cost but adding a cap will give mono/duo decks at least a small chance to defeat it (it will stay at the cap, but the creatures will hit occasionally), while it still does reasonably well against a rainbow (since the 8x quanta cost doesn't need to be changed). 80% was a random number I made up. I don't know how much it should be or if the inital cost would have to changed.