Well, in the abstract, of course, you are 100% correct.  If Estrada had pitched well, his team probably wins--but you could say that 'bout every starter, right?

Last season, that happened, they made the playoffs, did OK.  The very good starting pitching of last season, that was a 1-off.  It did mask many of the flaws of this team, that are now laid bare for all to see.  Slow afoot, overly reliant on power game to score runs, no ball sense, aging, poor fundamentals, don't hit much with RISP, questionable in-game managing.

As you noted several months back, this team is averaging 'bout .5 runs fewer/game compared to last season, that has to be taken into consideration as well.