Jon knows his range control far better than DC does. He's proven it as a champion against the best, Gustafsson included. Gustafsson had his jab to close, maintain and keep distance (and thus his range), while DC will not have this on his side to the same degree. If DC cannot get in relatively easily on Jon then he's screwed because in outer boxing range and certainly inside kicking range, Jon will fuck him up. Gustafsson had the length going for him (kicks and punches), footwork and range control of his own for this, along with the best jab in MMA to do the aforementioned (close, maintain and keep distance). DC does not have this like Gus does.
Now, if DC can jab his way in or manage to freeze Jon up from the distance to get in, when inside he can clinch fight Jon and almost certainly beat him there. He can hurt him in there and obviously take him down too. However, that's assuming he can close that gap relatively easily first, and likely a multitude of times, without taking too much damage, while still managing to work well inside there at that.
DC will have his work cut out for him because you don't just pass an 84.5" wingspan so easily without a great jab for entering (which he doesn't have), great teeps/kicks for entering (which he doesn't have), or the effective single or double leg shot (which he hasn't yet shown against high level competition in MMA).
If somehow DC can manage to get in, stay in, and repeat the process then he's practically guaranteed to beat Jones. I just know that it won't be as easy as he likely thinks it will be.