Jost is 15 months younger and has outperformed Roslovic to this point in their careers. There's almost no reason for the Avs to trade the better, younger player to a division rival.
He has?
Roslovic:
AHL 83 points in 97 games
NHL 38 points in 108 games
Jost:
AHL 7 points in 13 games
NHL 48 points in 135 games
Pretty close, not sure what kind of ice time Jost was getting but most of Roslovics would be 3rd/4th line with one small stretch in top 6. Neither are great possession players but a slight edge to Roslovic in that category as well. Pretty hard to see how Jost is definitively better.
Anyway, fair enough if you want to stick with your guy but they are very equal players at this point in their careers.