Pitchers throwing too many fastballs

I've never played baseball past third grade, but I've been noticing of late that our pitchers tend to get crushed when they throw fastballs over the middle and upper parts of the zone. Ex: Ferguson tonight.

Ferguson's curveballs were so good, it seems to me that they should throw less fastballs late in at bats and more offspeed pitches.

Does anybody with baseball experience agree?