Surprisingly, there haven't been many people complaining about this decision. Both guys have been great for the Jays in the second half, but if you look at the season as a whole:
Dickey 3.92 DRA, 4.72 xFIP but once again his ERA outperformed his xFIP which could be the case with knuckleballers. Also he seems to struggle in cold or windy weather which won't be the a problem tonight.
Estrada 3.40 DRA, 4.93 xFIP but I think it's clear he has an excellent changeup which (correct if wrong) may help him outperform some of his peripherals. When you consider the guy has a GB rate 10% lower than Dickey's in the bandbox of Texas there is a very good case for him being the wrong choice.
One thing to consider is that the knuckleball might have a better chance of being completely ineffective so maybe Dickey has a better chance of gas-canning, but I'm not convinced that's the case. Does anyone think Estrada is the wrong choice here? The season hinges on a guy who people have been waiting to blow up for months now, let's hope tonight is not the night!