Pikeru was saying that if everyone is using shade, the win % of players using shade would be 50% (since everyone's using it).
Anyway, to the matter of return and shade, I will say that in magic the gathering the card common to all mono-red decks are mountains. Since every red-deck win uses mountains, does this mean mountains are op? Shade and return fall into this category imo; ie, they're not cards that are widely used necessarily for their power, but because there's nothing else to use and/or they fill a niche role that is very important to the function of their respective files. Shade is widely used because lawtia doesn't have any other lvl 1s worth using in the average lawtia file, and a file that doesn't use lvl 1s will most likely have poor SP flow. Return is widely used since it affects the most common unit type in the game (lvl 3 units), and the falkow strategy is, "isolate and destroy." All the other falkow grims either require specific file types, or don't help with the general strategy. It also doesn't hurt that every new player starts off with these 2 cards, so it's no surprise that they're widely used.