Tanev is not worth much seriously.
Tanev is 26 and is a great defenseman. His limited offensive abilities certainly hinder him, but that doesn't mean he wouldn't be the perfect partner for an offensive defenseman that had limited defensive abilities. If Tanev could play the left side, he and Barrie would be a good 2nd pairing.
The downside is that from the Avs, Tanev isn't exactly worth Soderberg. He's also not worth trading Duchene, Landeskog, or MacKinnon. The Avs don't really have an in between player that would complete that trade.
As far as Landeskog vs Tanev value wise.. Landy is younger, better offensively by a wide margin and just as good in his own zone as Tanev is. Landy holds more value to the Avs in that he's not only the more complete and better overall player, he's also the only winger we have that is a proven top 6 player.