Salary has always been 100% part of the Tavares debate because the success or failure of Tavares will have a very large impact on whether this era can produce a championship. If he's giving us 2018-19 numbers over the bulk of the contract, we have a great chance. If he's in a gentle decline, it depends on how we can average down his salary (like with Simmonds, Spezza and Thornton) to make it work. If he has a sharp and dramatic decline, the Leafs will be severely challenged to upgrade other key positions.
The Steve Yzerman transformation narrative is fine as a general guideline, but the trouble in believing it as gospel here is Detroit probably could have just as easily won if Yzerman had stayed a 100 point scoring beast in 1997 and 1998. As we move later into the 2002 run, you're basically talking about a 37 year old with shredded knees trying to get every last ounce of hockey left in his body. John Tavares is 30 years old right now, so the decline and transformation is coming at an inconvenient time. Tavares has also never even approached Prime/Peak Yzerman, so that Yzerman transformation doesn't fit that well if Tavares is going to become a much diminished defensive specialist.
At this point, I'm just hoping he gives us 35 year old Patrice Bergeron hockey for the next few years, try to hit that championship goal.