Breaking down Alexander Romanov's game
The Islanders used Romanov in essentially the same situations as Ryan Pulock. He started 29% of his shifts in the offensive zone, compared to Pulock's 27%, and 36% in the defensive zone, compared to Pulock's 38%. They both started 35% of their shifts in the neutral zone. (These stats, courtesy of EvolvingHockey, do not include shifts started on the fly.)
By some advanced metrics, Romanov was the worst defenseman on the Islanders, but there's more to the story. When he was on the ice, the Islanders scored just 46% of the expected goals, but 53.5% of the actual goals. This usually happens when players are unusually good at shooting, but Romanov and his 2 goals might not fit that description.
Another possibility is that the Isles have amazing goaltending, and everyone on the team performs better than the expected goals would indicate. This would make sense, but it's not true - Romanov, Noah Dobson, and Ryan Pulock all have large gaps between their GF% and xGF%, but Adam Pelech, Scott Mayfield, and Sebastian Aho don't.
Whatever the reason, it's undeniable that the Islanders play well when Romanov is on the ice. This was especially true at the end of the season, once he began playing on a pair with Ryan Pulock - in Romanov's final 18 games of the season, all of which he spent mostly with Pulock, the Islanders scored 65% of the goals when Romanov was on the ice.
So, what's our take on the trade one year later?