I had this same thought, then I found Virtanen's fancy chart from McCurdy and I'm much less concerned with that. Virtanen is a strong play driving forward analytically and I think he could be a good replacement for Rust down the line, if they decide to let him walk.
My concern is that they'd leave McCann exposed to protect Virtanen, which I wouldn't be that thrilled about. I also think it's worth pointing out that there were some unflattering rumors about Virtanen and McCann when they were on a team together in Vancouver. I would hope they would have matured by now, McCann definitely seems like he has but I've heard negative stuff about Virtanen off the ice.
He also had 36 points in 69 games last year, which was more than what Gurianov had. He's just having a bad year this year.
I think he's probably only a 30-35 point guy normally, probably like 25 ES points and 5-10 PP points a season if I had to guess. But that combined with his size, analytics and physicality results in a pretty solid 3rd liner IMO.