It's not simply a 1-for-1 player swap analysis. Cole and Zadorov were both light years ahead of guys like Forbort, Desharnais, and Juulsen in terms of their ability to move the puck, and generally function on the offensive side of centre ice. Couple that with Soucy and Myers taking a major step back from last year and you have a total meltdown.
Sure, the forwards aren't gunning as hard as last year, but I think most of the offensive problems are back-end driven because in a "best case scenario" four of your six defensemen handle the puck like a grenade. In a "not best case scenario" you have one depth guy in Brannstrom (who management stumbled into by pure luck, and who was not in their plans) that can actually make a pass, and then all of them handle it like a grenade. I don't think you can overestimate how badly this lack of transition game can impact your ability to generate shots and offense.
The only way they were able to moderately function offensively was by playing Hughes/Hronek like 25 minutes per night.