Janmark can kill penalties and do other things and Lavoie can't.
Brown on GYB nailed it. Lavoie simply won't be put in a position to score due to the volume of guys ahead of him in the lineup that can do it better than he can. He's not killing penalties. He's not winning defensive matchups. He's not an energy/role player.
Other than the principle of losing a player on waivers being offensive, I am struggling to think of what the actual consequence is of losing Lavoie. We don't have a guy who's feature skill is scoring, but is probably around 7th or 8th (generously) in line as far as that ability on the team goes.
His skills package is dime a dozen and if we lost him I don't know if we even attempt to find a replacement because we already have what he brings. He's basically Brendan Perlini and we don't need that.
Regarding the bold. Janmark and Brown combined for 8 goals last season. I know Oiler fans have a hard-on for that Janmark-Henrique-Brown 3rd line because of like 5 good games in the playoffs, but lets not pretend like those two wingers are a sure bet to be legit top 9 forwards all season. Would benefit having someone who can move up and contribute some hypothetical offense if one or both of those guys slump for an entire season again.
And in terms of not killing penalties, winning defensive matchups... neither is Corey Perry. And frankly, with no disrespect to Perry, I see Lavoie just as capable of filling an energy role as him at this point in their respect careers. It's not like Lavoie is afraid of using his body out there. Limited sample size, but he threw more hits/60 than any player on the team last season other than Adam Erne. Hell, he's not even afraid to drop the gloves if need be.
This kid took $140K less than he could have if he just accepted his qualifying offer for goodness sake.
At some point you need to reward prospects in your organization who do everything you ask of them.
Let Corey Perry ride the bench and play on the 2nd night of back to backs or when someone is banged up. Frankly what the Oilers should be doing with Perry is waiving him but have him stick around and only "calling him up" on days that he's actually going to play in order to maximize cap savings.