Marner got knocked around in this series and was not as effective as he was in the regular season, but you have to keep in mind that this is his first season and even Patrick Kane needed more than one season to learn to become real good.
I know you have this obsession for Hanifin and I haven't watched enough of him to form an opinion as to who's better between him and Marner. Based on stats alone though, I'd say Marner's were more impressive than Hanifin's first year stats. Yes defence matters, but so does offence. Coaching can teach how to defend but you need pure skills to score that cannot be taught.
The Canes have the opposite problem as the have huge holes up front but solid on defence. They seem to have put more emphasis on drafting defence vs the Leafs' drafting offence. Maybe circumstances and availabilities of talent at the time played a big part. I can see a match for potential block buster type deals between the clubs.
The Leafs have an abundance of young forwards in Sashnitkov, Leivo, Kapanan, Lepsic etc. who are NHL ready but there may not be enough room to fit them all in next season. They may be trade baits to land one or two solid physical d men who they desperately need.
