The record according to the WFDF is 134 kilometers per hour,
or 83 miles per hour.
That’s nowhere near a ML fastball. And keep in mind it’s a record, so your average person, throwing as hard as they can, is nowhere near that.
Looking at the physics makes it clear that frisbees aren’t going to be very fast – they’re purposely built with a fair amount of drag from the wind (that’s how they get lift), and they’re light enough that they don’t have a lot of momentum to overcome the drag. Just the opposite of a baseball (or bullet).