I don't have any concrete data to back this up but I don't see where Hossa has suffered the same head trauma that Toews has. Hoss also plays wing which is a less physical position for the most part and Hossa tended to shy away from being a heavy player. Don't get me wrong as Hoss is and was a warrior and we miss him terribly but I still see Toews as having tougher minutes overall during the past 9 years. ( even with being on the same line primarily )
I'm just trying to find the logic to Toews' decline and you brought up Hossa which is a good point to consider give they played on the same line and Hoss is a good 5 years older or so ...
I do think however though some wingers do play physical ( not Kaner! ) and Hoss did battle like a true warrior I still think the center takes a little more abuse in front of the net with in particular cross checks to the shoulders & neck/head. That repeated abuse on the spine and nervous system will take it's toll. I just seem to recall Hossa playing less heavy meaning he didn't go crashing into the boards at every opportunity ... don't get me wrong as he is a battler but he played smart as he knew how to play hard without risking his longevity.
For one: Hossa got obliterated by Torres. I don't think Toews ever took such a severe hit--not even from Willie Mitchell.
For two: There was only one season where Hossa was 2nd to Toews in Defense: 2013. Every other year Toews was balanced or slightly more O, Hossa was the D anchor.
For three: Hossa did indeed go into the boards, and fought guys off the puck--more into the boards than Toews but Toews indeed played the netmouth more.
For four: Hossa was the only forward with any regularity to beat out our D (back when our D was actually good) on the odd-man rush, bailing them out.
For five: When Datsyuk pick-pocketed Hossa, Hossa actually went and got the puck back.
For six: When Toews had an early exist in 2008, Hossa played in the SCF.
For seven: When Toews & the 'hawks got jacked by Detroit in 2009, Hossa played in the SCF.
For eight: Hossa's more than 5 years older than Toews--more like almost 9 (04-88 vs 01-79)
For nine: Hossa managed to bounce back in 2017 from a disappointing 2016. We're still waiting on Toews.
For ten: Hossa's borther made it further in the NHL than Toews' (okay, yes, i'm reaching here
)
Seriously though, any disparity between Toews and Hossa in terms of hard minutes is not that great, which either means that Hossa is/was more resillent than Toews longterm (for whatever reason), or there's just something else afoot than simply "hard minutes". Kane being pure O makes sense that the dropoff of Toews with respect to Kane makes sense. Hossa? Not so much.