I agree with you regarding his points output in his last 2 full seasons but his plus/minus is not that impressive leading to the perception that his defensive game suffers because of his offensive upside Where he tends to get caught up ice on breakaways!
However, where he does come off as distinctly second best to Fournier is in the goals column.
For me, O’Connor is more of a set up man on the pp and a d man with a good outlet pass, in other words, exactly the role we’ve brought Matt Register here to perform!
If we’re looking for a replacement for Fournier’s goals, (and I’m not sure we are), in Fournier’s last 2 seasons with Devils he scored 37 goals in 106 games.
O’Connor, in his last 2 seasons for Sheffield scored 10 goals in 90 games!