Lets go through some of the players that the OP named:

Erik Karlsson - That was probably the best playoff run I've ever seen from a non-goalie ever. He was incredible. Looked like the best player in hockey for a 19 game stretch.

Bobby Ryan - He scored at a rate that he hadn't scored at in 6 years (15 points in 19 games - a 64 point pace). To actually expect that out of him is delusional.

Derek Brassard - Produced at his career average rate. He was an important role player, but he was just that, a role player. Every team that goes on a deep run has a Derek Brassard. Nick Bonino, Tyler Bozak, Charlie Coyle etc.

JG Pageau - Had 4 goals in a game vs the Rangers. Scored 6 points the rest of that run.

Marc Methot - The typical mediocre defenceman that gets elevated during a playoff run. Ron Hainsey, Brooks Orpik. These guys were bad to meh before and after their playoff run.

Dion Phaneuf - Solid second or third pairing guy to have but nothing spectacular. This is another case of fans overrating a guy that pretty much every team has.

Craig Anderson - Up and down career. This was one of his up years but he's never been particularly thought of as anything more than an average goalie.

Clark MacArthur - This dude had not played in two season (8 games combined) due to major concussions. The fact that he even played is a minor medical miracle.

It would be pure revisionist history to claim that the 16-17 Sens were anything more than a Cinderella Team. To call them a contender is 100% delusional. For a team like the Sens to go as far as they did, they needed a ton of luck and their players to get hot which is what happened. Which is also what happens to every team that has a deep run.