Barring any major injuries you know you'll get the following from these guys
Stamkos will score 30+ goals
Malkin will put up 75+ points
Ovechkin will score 30+ goals
Bergeron will put up 50+ points
Chara will put up 40+ points
Iginla will score 30+ goals
You can't say that right now about Seguin. While everything points to Seguin elevating his game to the next level, it doesn't mean he will. The guys listed above are established, you know what your getting. Someday Seguin will get to that level maybe another 1-2 years but right now you don't know what Seguin will bring to the B's next season.