I've seen McDonald's slider, curve and change all rated as plus pitches. They're better pitches and he's throwing them more this year because he's controlling them better. You call his fast ball average, and two of this off-speed pitches plus pitches, notice that McDonald has improved his command, and you have a #2 pitcher, unless this is just a streak instead of a breakout and he regresses back to the guy with #2 stuff but doesn't throw it as well.
McDonald's stuff has never been an issue, he had the best stuff on the staff last year, his command/control and pitchability have been the questions. I stated his velocity because he certainly doesn't sit in the mid 90s. Lastly, it has been 9 starts. Yes, he has shown improvements, but it has been <1/3 of the season. If everyone was counted as a " " starter off their best stretches of 9 starts, I would hazard a lot of pitchers would be considered 1s and 2s.