If he'd given the penalty try earlier you'd then be complaining that he gave the penalty try to early. Was that maul legal?? Do you actually play rugby?! That's a textbook maul! There's no interpretation needed there, only rudimentary knowledge of the laws of the game. I agree that often cards are handed out too easily, but here I feel that both were deserved. Especially the second.
Sorry but both those yellow cards were earned by the idiotic Welshmen who received them. You point out Biggar's, it could hardly have been more obvious that he was bringing the maul down! Watch it again. He grabs the saffer and then just pulls him to the ground. Thats a penalty anywhere on the park except 5-10m from the line, which it was, and after being pinged for infringements around the maul at least 4, 5 times in the previous few minutes.