That's not really "a system", that's how marginal pricing always works for fungible goods. If you need to buy 100 units of something, and the guy selling next to me can't go any lower than $10 without selling at a loss, I'm going to sell at $9.99 every time. Why would I do otherwise?

The point of this is that it's supposed to guarantee windfall profits for wind operators, to make it attractive to keep building out wind until all the marginal gas is pushed out of the market mix. The price being set by the highest-cost source in the mix is a feature for incentivizing buildout, not a bug.