If that's true, it's very interesting, as it means other marquee riders such as Vanmarcke, Phinney, Rolland etc must be on relatively low salaries...
It isn't surprising.
Vanmarcke is a rider with limited skillset and can basically shine only in cobbled classics (unlike riders like Sagan or Van Avermaet that are more likely to take decent wins all year), but he hasn't won any significant one since 2012 Omloop, so he can't demand the money that better all-rounders or riders with big wins can demand.
Phinney is an obvious case. Due to his injury he has not delivered the promise he was giving early in his career and is not that likely to ever deliver that TBH.
Rolland's market value has definetely dropped since other French hopes like Bardet and Pinot stepped up. He is considered now just 3rd or 4th best French climber and not really a podium GC material in GTs, so he is just forced to find his niche and can't demand to be paid like a next big thing.
This is just what Vaughters is forced to do with his budget. Try to glue together a WT-worthy team out of riders who haven't done enough in recent years to demand big contracts from other teams. I guess that is not an easy task and the results and performances that Cannondale has delivered this year deserve some respect considering the circumstances of "running on the ragged thin edge of really being able to carry on as a WorldTour team".