Zharovsky is 6'2, skilled as hell, smart as hell with the puck on his stick, has very good puck-protection technique, shoots well, is an above-average skater, and has tons more room to grow physically, and you think he's only a "good" prospect?
If true, there are decidedly very little teams that have "great" prospects in your opinion.
I think the trade of Knies for Zharovsky and two first-round picks hurts as a Canadiens fan, but is more or less fair as of this season.
But if Zharovsky continues showing crazy progression, as he did from his draft year to his D+1, it very well could be that in a year or two Zharovsky would hold similar or even higher value on his own than Knies, without even mentioning the two first-round picks.
The one reason why the Canadiens would do that trade is that they need top-6 help right now, not in 2 years, and also to ice more space-generating physical players, like Knies, to compliment the skill guys they already have.
All of it is a moot point now though, given that the Leafs will likely not trade Knies to the Canadiens unless they get immediate quality help back, which would mean that Zharovsky would not be part of the package.