Wang is pretty good, he is not 19 wins/per year good, but certainly not as bad as his current record suggests.
Wang may not see 19 wins again (look at Mussina, how often does he get 19 wins or 20 wins?) but should be good enough to get 10-15 wins consistently on a good team.
I was just watching ESPN baseball news and one question was should Wang be in the rotation or in the bullpen. The analyst says based on the game against the Nationals, Wang should stay in the rotation because Wang is getting sharper, and based on his previous season's performance, Yankees ought to be more patient with him.