I disagree! I call a fastball, a fastball, not because of the speed, but because of the spin. I also think calling a drop, curve, rise an "off speed" pitch is inaccurate, as I believe all pitches should be within the same few mph of each other. Except, a change-up, my rule is if a novice spectator knew the pitcher threw a change (probably due to slowed body speed), it's not an effective change-up.
I too love a good over the top drop, thrown properly with spin, rather than body tilt, etc. But, the pitcher can't confidently throw that pitch without an extremely talented catcher. It would get passed an average catcher, the pitcher would know that, and not be able to confidently throw that drop.
I'm not a fan of a peel drop, it just doesn't move much. Why bother? Although, I'm sure some pitchers have been extremely successful with it.
Throwing a drop to induce a grounder due to topping the ball, a swing and miss due to vertical movement, or whatever gets the fielders an opportunity to make an out, is a successful drop!