I think you make a valid point. The warmer the winter, the thinner and warmer the resulting ice. When it comes to the melt season, thinner, warmer ice will start to melt sooner. When you add the warmer summer, plus all the heat the ocean is absorbing globally (and the arctic ocean in particular absorbing ever-warming runoff from the continents), you get more melting. As the polyna's become larger, the water absorbs even more heat -- a positive feedback. All of these processes are ongoing -- every year a "little" more heat is added to the global system. (E.g., June had the largest SST anomaly for any month, ever.) That's why I don't see any slowdown in our future -- at least until and unless global warming reverses.