Workload seems to be the constant concern here, for DJ. Lets look at the other potential #1 RB's, especially those slated for "Bellcow" status...
Gurley - well established, all world talent, but the offense is just bad. As has been mentioned, no matter how many touches Gurley is slated for, if they can't sustain drives, and score points, it will negatively impact him.
Elliot - Rookie, while the industry is excited by the possibility of him accumulating 350 touches, behind that monster OL... we have no track record to look at. Whether you want to admit it or not, it's a gamble. While some feel like this is can't miss, I can immediately see a potential scenario that tosses a wet blanket on him. Suppose, like many rookie backs, he struggles in pass pro. Dallas know's they aren't winning anything without Romo, and they have a couple viable passing down backs on the roster.
AD - He's 31, and has never been much of a pass catcher.
Miller - Miami seemed to be willing to put the security guard behind Tannehill in order to keep Miller off the field. While I believe in Miller's talent, there are certainly red flags that you can point to that may indicate he isn't cut out for bellcow status.
Bell - 4 game suspension looming, and missed time to injuries in 2 of 3 seasons so far.
Charles - coming off of his second ACL surgery, and his backups displayed they can hold down the fort last year.
Freeman - Second half fade, combined with Coleman, point to a reduced workload.
Ingram - Injury history, and team has a history of RBBC
and on, and on, and on....
Do I buy all of those risks? No, but they all deserve some consideration. The point is, every one of the top RB's has something about them that could cause you concern for workload, or performance. I don't think DJ's risks are any more, or less, pronounced than many of those I just listed. Someone has to be the top RB taken however, and DJ is a guy coming off of an extremely strong finish to the previous season, in a fantastic offense, and seems to pass the eye test. All of the conversation coming out of Arizona has been positive, in regards to his performance thus far in camp, and pre-season. If I'm taking the first RB off the board in a draft this year, I figure DJ has as good a shot as anyone of returning value on that pick.