For what it's worth, Grayson is not bigger than Herro. They have pretty identical heights and weights. They have different strengths and are completely different players. I'd imagine they Jazz wouldn't draft him if available unless they were sold on Herro being a great shooter like Klay Thompson.
Herro is similarly ~ 6'5" with shoes like grayson but his wingspan (taken from Kentucky's preseason pro day measurements) is only 6'4.5", he's got smaller hands, a really poor max vert at 33.5", and despite being listed at 195 lbs, definitely doesn't look it as his body fat is also quite high. The body weight/fat can and will change, but he's got really short arms, and i don't know how much more explosive he will get even with training. he's not close to the athlete grayson was at the same age or is now, but overall you're right in that they are different players. I'm not enamored with the comp, but I guess he could be a smaller version of klay since they are both just average athletes and get most of their offense off quick jumpers and very few dribbles. The other comp people have said is booker which I can see some of in his game as well, but he won't be the iso player that booker is at the nba level. I don't think he can be an on the ball guard like grayson could be as a secondary ballhandler/creator. I still think grayson can be ginobili-light w/ better shooting.