Defencemen develop their defensive game slowy.... Offense is typically a skill that is there, or not.
You look at current NHL D, and their stats in their rookie campaign in the AHL.
John Carlson - 19 year old AHL Rookie year. 39 points in 48 games.
Karlsson - 19 year old AHL Rookie - 11 points in 12 games
Subban - 20 year old AHL Rookie - 53 points in 77 games
Krug - 21 year old AHL Rookie - 45 points in 65 games
Tyson Barrie - 20 year old AHL Rookie - 32 points in 49 games.
Sure, offense can take time to develop in the NHL, but in the AHL, Elite offensive D, show their numbers in their first seasons.... Granted, Lilly is younger than these guys, and patience is needed... let's see what he can do with more ice time, as a 19 year old to start the year. And note... this is a discussion over the term "ELITE"... not good, or very good... but ELITE. As
@613Leafer has said... if we get a very good Defensive guy, with average Offense skills, that a great player to have on our team.