Well, that's not totally true. Certainly not for Toews.
Yes, he's had some great linemates. Since 2007, the guys he's played most with 5v5 have been in order:
Kane (3504 minutes)
Hossa (2763 minutes)
Sharp (2635 minutes)
Saad (1303 minutes)
But then you think about the rest of the guys he's been stuck playing with at various points in his career, and still been a possession superhuman as well as a consistent high-end (albeit not elite) producer:
Troy Brouwer (1021 minutes)
Kris Versteeg (914 minutes)
Viktor Stalberg (692 minutes)
Dustin Byfuglien (563 minutes)
Bryan Bickell (318 minutes)
Martin Havlat (253 minutes)
Andrew Ladd (248 minutes)
Tuomo Ruutu (247 minutes)
Andrew Brunette (200 minutes)
Tomas Kopecky (160 minutes)
Michael Frolik (137 minutes)
The list goes on, all the way to Brandon ****ing Bollig.
http://stats.hockeyanalysis.com/showplayer.php?pid=649&withagainst=true&season=2007-15&sit=5v5
And pretty much every single guy on that list saw not only significant, but stratospheric gains in both their production per 60 minutes and their possession numbers when they were with Toews vs without.
Let's put this in perspective. So far this season, Toews has a CF% of 52% and a GF/60 of 1.69.
...In 2012 Jonathan Toews dragged the gradually cooling corpse of Andrew Brunette to a 55.6 CF% and a GF/60 of 2.10.
Nobody Stan could find on the market for the 1LW slot could be worse than 2012 Andrew Brunette. Nobody that has played on Toews' wing this season is worse than 2012 Andrew Brunette. But Toews was better with Andrew Brunette in 2012 than he is this year.
Why? Because the issue is with Toews. The LW is a convenient excuse. If Toews was playing up to the standards of Toews we know, the possession super-human that drives play like few in the NHL, then this '1LW problem' doesn't exist. Because the 1st line would be producing at a good rate with anybody, from Tikhonov, to Dano, to Garbutt, to Bickell, to Micheal ****ing Rozsival dressed as a forward. But he's not playing at that level. I don't know why. I don't think it will last forever. Frankly, I think he's been quietly improving.
Obviously bringing a good, useful player into the lineup will make the team better. But anybody who thinks the LW is why Toews is struggling has got the equation backwards. Whoever is put on that LW will struggle, because Toews is struggling.
And when he and Hossa come out of it, whichever interchangable part is lucky enough to have been assigned to the 1LW slot at that time will get a whole bunch of undeserved accolades for 'fixing' the issue.