Roslovic is a winger, and he played top six wing last year with guys like Ehlers. Howden also got significantly less ice time, and no power play time. Howden plays center, is a lot more physical, and is a guy that can mold his game like WPG's Lowry to carve out a role for himself. In other words, their underlying 5v5 production is a lot closer than it looks. Roslovic scored 6 extra 5v5 points, while getting 200 minutes of ice-time at 5v5 with high skilled players.
On their production levels from last year, it's actually a very fair deal.
It's essentially trading for a guy in Howden who is a current NHL 4th line center that can be groomed to replace Lowry as far as WPG's upside, or a two-way LW that can slot into their 3rd line. With Roslovic, WPG probably knows that he will not be an NHL checker and hasn't proven to be a scorer even after getting top 6 and power play minutes... who has already asked out of the organization.