James Van Riemsdyk scored 36 goals last year. Suggesting that he is relatively insignificant is just wrong. I realize that he isn’t anywhere near as effective as Tavares and he probably doesn’t contribute as much as his numbers say but losing him won’t just be some seamless transition.
Frederik Andersen led the NHL with 2211 shots against and he still posted a stellar .918 SV%, despite also posting a 2.81 GAA. A .918 SV% and 2.81 GAA generally tells you that goaltender’s performance isn’t sustainable. At 5-on-5, Toronto was top-5 in shot attempts against, unblocked shot attempts against, and shots on goal against.
Tavares and the rookies may be able to more than make up for the loss of JVR and Bozak, but in my opinion, their defensive performance and their goals against last season was not sustainable.
I don't think you can do the arithmetic straight across with JvR + Bozak vs Tavares because of the structural changes adding a centre of JT's calibre allows. Suddenly you've got Kadri on the 3rd line, you no longer need to move Nylander to center ice and can keep him riffing with Matthews, the average quality of competition goes down across the board, and Marner doesn't have to be the driver of his line, though credit to him, he seemed capable. JvR's netfront ability will be sorely missed, more than most Leafs fans are comfortable admitting, but you've got all these peripheral improvements by adding JT that will I think pull this iteration of the Leafs ahead. Of course, given their age, you can probably expect natural progression out of Matthews, Nylander, and Marner as well, but how much that will be offset by a new scarcity of ice time is anyone's guess.
Something interesting about Andersen -- of all shot locations he faces, the area he most outperforms the league average is in high danger chances in close. Counterintuitively, his save percentage on less dangerous shots is pretty pedestrian. I'm not sure what that means exactly, but it may suggest that he's more systems-independent than most goalies, which would make you think that his performance these past two years is pretty in line with what he is and what you can expect. But I'm not that confident in that take and of all the avenues for catastrophe next season, him underperforming would surprise me the least.