I have nothing against the argument that you presented, and nothing against the stats that you quoted. They are all good stats to use and, as always, the more you look at, the better the story you'll get. I'm not sure that one particular stat is clearly better than any of the others.
That said, Siera and xFIP are the two best predictors of future ERA. If I were going to make a bet on who will be our best pitcher going forward, I would go with Price, then Porcello, then Wright, in that order.