It's annoying i can't filter hockeystatcards.com to see just what the players contributed to the leafs and not the total after they were traded too, but let's look.
Last year actual total net rating from hockeystatcards.com ---> last year's rating plus last year's preseason projection paced to 82gms
Note that the 2nd set of stats is for a mostly healthy full season, so you might want to subtract some of that projection and replace it with sub-replacement level replacements too.
Matthews +11.84 ---> Matthews +21.0
Nylander +9.27 ---> Nylander +12.5
Knies +1.54 ---> Knies +5.1
Tavares +8.13 ---> +9.4
McMann +1.01* --> McKenna ?
Maccelli +0.10 ---> Roslovic -1.4
Laughton -2.99* --> Paul -5.3
Cowan -1.88 ---> Cowan -2.3
Joshua -2.02 ---> Joshua -5.1
Roy -6.07* ---> Sissons -7.8
Robertson -4.62 ---> Blueger -7.3
Domi -8.48 ---> Duhaime -7.3
Lorentz -5.11 ---> Lorentz -7.6
Jarnkrok -8.45 ---> ?
Groulx -2.22 ---> ?
Quillan -5.07 ---> ?
Haymes -2.25 ---> ?
Blais -0.85* ---> ?
Tverberg -1.41 ---> ?
Pezzetta -3.06 ---> ?
McCabe +1.44 ---> McCabe +2.2
OEL +1.02 ---> OEL -0.4
Rielly -4.10 ---> Rielly +0.6
Carlo -3.85 ---> Raddysh +9.3
Stecher -5.89 ---> Tanev +2.5
Benoit -14.1 ---> Andrae +6.0
Myers -8.61 ---> ?
Tanev +0.43 ---> ?
Benning -1.27 ---> ?
Villeneuve -1.30 ---> ?
Rifai -1.86 ---> ?
Thrun -2.17 ---> ?
Mermis -2.50 ---> ?
So actually the Leafs come off looking even more improved than this article says, as long as the new roster performs around the average of last year's performance and last year's preseason projected performance.
The biggest uprades looking at that would be:
1. Andrae over last year's #6 slot
2. Raddysh over last year's #4 slot
3. Matthews bouncing back to elite again (though not back to super elite)
4. Tanev over last year's #5 slot
5. McKenna over last year's #3W slot