Here's a head to head comparison of Backlund vs an unnamed player from another team (revealed at the bottom of this post, along with which team is which).
When these players are on the ice, here's how their teams have done:
Team A: 61.03 CF/60, 52.27 CA/60 (53.87%). 57 GF, 37 GA (60.64%, +20)
Team B: 61.60 CF/60, 51.15 CA/60 (54.65%). 36 GF, 28 GA (56.25%, +8)
When they are off the ice, here's how their teams have done:
Team A: 52.51 CF/60, 55.35 CA/60 (48.68%). 68 GF, 74 GA (47.89%, -6)
Team B: 53.10 CF/60, 54.13 CA/60 (49.52%). 65 GF, 79 GA (45.14%, -14)
So, looking at those stats, both Team A and Team B have the puck a lot more when Backlund/Player X are on the ice, generating about 15-20% more offensive shot attempt while also reducing the amount given up. And as a result they have positive goal differentials, both teams over 20 goals stronger with the player than without, achieved sustainably through having control of the puck.
When these players are off the ice, both teams have struggled comparably. They're outshot and out-possessed, and as a result have negative goal differentials. Team B also generally has weaker percentages than team A, although they're slightly better in possession.
If you haven't guessed, Team B is the Flames with and without Backlund. Team A? The Oilers with and without Connor McDavid. Calgary with Backlund is comparable to Edmonton with McDavid across a variety of different metrics. And, Calgary without Backlund is comparable to Edmonton without McDavid. Backlund is absolutely essential to this team.