This is a bullshit narrative if ever there was one.
One incident did not define that series, bad goaltending, bad and panicky defensive play, and an overall lack of depth did the Avs in. The difference is not going to be felt with players like MacDerrmid, but rather players like Lehkonen, Cogliano, Helm, Manson, and hopefully, Kuemper. Also addition by subtraction with Graves and Nemeth (and Grubauer) being gone.
The two things I will freely admit a goon does to help his team is allow for the perception that they are now "tougher" and embolden them to play with more confidence during the regular season and the energy a good brawl and/or a big hit brings to a bench, especially if you're looking to change the momentum. That's great and all for the regular season, but you don't need pickups like that for the postseason. If you ain't engaged and playing hard-nosed hockey by the time the regular season ends, no goon is gonna help that.
The last thing the Avs need to get into is a war of attrition against the Blues. That's what the Blues want. They WANT the Avs to get distracted and throw down, and form an assembly line to the penalty box. Avs just need to play their game and get to the net as much as humanly possible. They did an excellent job, especially 62 and 13, in disrupting the Blues' attacking zone cycle. All St. Louis could do was a lot of one-and-done rush attempts (which admittedly the Avs gave up way too many and need to play more aggressively in the NZ).