Forsberg had himself a better PPG rate in 2021-22 with a combo of Ryan Johansen and Matt Duchene as his centers for 42-42-84p in 69 games played.
His 2023-24 41-42-83p in 73 games is going to net him career highs, but it's unless he puts up big point totals in the last 9 games of the season, he's not going to improve on the pace he scored at 2 years ago with 2 players Nashville bought out/paid to ship out of town this past summer.
At best, Forsberg sets his new highs with an extra 5 games played by scoring 2 points in game 74 - comparing this season's point totals where he hasn't missed any time to a season he missed 13 games doesn't really make for a good apples to apples comparison the way you've stated it.
I think it's unfair to credit ROR with Forsberg's production this year, as he produced at a higher scoring rate with inferior centers previously 2 years ago. I cannot deny that ROR and Forsberg seem to be meshing, but I think Forsberg is revitalizing ROR, as opposed to ROR elevating Forsberg.
ROR played well in Toronto after his trade last year, but he didn't elevate his linemates there the way you imply he's doing in Nashville. Had he done so, I'd think Toronto would have found a way to sign him to some kind of deal to stay there.