I've vacillated on Johnston this whole draft season.
If playing WR is about getting open and catching the ball, he's not really a clean projection on either. Not much separation on tape, poor contested catch percentage, and he had several easy drops.
Physically, he looks exactly like a less rocked-up Dez Bryant. 4.5 speed, otherworldly burst, zero change of direction, all fueling a plant-and-go playstyle. Both of them broke a wild amount of tackles for 6'3" receivers, because they can go zero to 100 instantly.
I think you can justify a gamble on a poor man's Dez at #24. And he's the kind of sideline complement that I'd want to have for a slot god like CeeDee. But it's still a gamble, cause he's not really polished on a lot of WR fundamentals. He cheats it in college with superior athleticism, but he's not athletic enough to play sloppy and beat pros.