The key component traded for two first line players. That is not a negative.
Quenneville had it out for him. Guys like Danny Briere got the same treatment early in their career by coaches who didn't like them.
The only player with higher upside in the organization that wasn't a regular last year is Connor. Yes I'm including Petan and Armia in that. Dano has great offensive skills as is shown by his charts. He finds the soft areas of the ice real well. Makes very nice reads with the puck and without it as well. Very high hockey IQ. Skating is still a bit choppy and needs some work on positioning, but can be sneaky effective at stealing the puck in all 3 zones.
He should be minimum a 3rd liner to start the year next year. His pts per 60 was higher than Armia, Stafford, Petan (6th on team if you discount small sample size Kosmachuk and traded Ladd). His goals per 60 trailed only Scheifele, Wheeler, Little, Stafford, and Ladd. Dano only trailed Perreault, Wheeler, Byfuglien, and Scheifele (discounting small sample size Cormier) in Shot Attempt Rel %. By every metric he is ready to step onto a 3rd line and move up to a top 6 role with PP time next year. He blew away guys like Petan, Armia, Burmistrov, Lowry, Copp, etc in ALL respects (that includes physicality and grit).