You do realize that probably half of all NHL dmen were big time offensive defensemen when they were 18-19? You ever watch EJ, Leo, Ballard, Goligoski, Suter, Faulk, Leddy play in the WCHA? Just because the kid is able to carry the puck doesn't mean that's the only way he can succeed in the NHL. The kid has all of the physical tools, what appears to be a great attitude,and a very good work ethic. His numbers in Junior have been fine, especially when you understand that he spent all of last year trying to tone down his "run and gun" to try and round out his D.
Thinking that Dumba can only become one of the 3 options you list is laughable at best.