Yes Iowa does not possess great speed at WR. Marvin had good speed, but even he is a bit of a strider.
KMM, KD both long striders. Nothing wrong with that, unless that is all you have. They have the ability to blow the top off possibly, but something to be said for more explosive quickness off the ball, and in and out of cuts.
That's why you saw GD talking about motions and bunch formations. Some way of trying to manufacture separation against man coverage.
If you can't create space vs. tight man you are in trouble. Which we were last year against teams that could play tight man. Nobody can get open, extra man in the box against our poor run game, and an extra pass rusher. Not a good recipe for offensive success when the other guys can lock you down with man.
Timed 40 can give you some measure, but realize that is withou pads, on grass, and minus several months of very specific training to run a fast time in that exact scenario. Obviously it doesn't always precisely correlate to football speed.
I believe that is also why you will see multiple TE packages. If you can't outrun them, or create space you at least try for a physical mismatch or dictate defensive personnel and/or structure to account for your personnel on the field.
Our receivers are not explosive. Greg Davis is smart enough to realize their limitations and scheme around that.