Sure, but that's why the league has a soft cap. Your contracts are never going to add up to a clean 100% on a team that's trying to be competitive.
Ben said it himself at the time of the deal, that is the going rate for new contracts for players seen as key bench players. When you take a look around the league's free agents each summer, that line of thinking is accurate more often than not.
I like Ben. He has good internal sources. I tend to agree with most of what he says about fit, players, etc.
That said, I'm not sure that the Cavs have a good handle on what the actual market value is for players league wide, I think Ben's understanding of market value comes from the organization, or worse, that player's agent, and I tend to think that both overrate what some of our players would command on the open market. Drummond turned down a $20M per extension offer from the Cavs and is currently playing on a league minimum deal. TT asked for a max extension here, signed a two-year deal for the MLE with Boston, was traded after a single season, and is generally considered to have negative value - on an MLE deal.
There's no evidence to suggest that any other team was prepared to offer Lauri the contract he got with the Cavs and substantial evidence that his other offers were lower. The Bulls clearly didn't want to pay him that much, the Spurs likely didn't want to pay him that much (he'd be the highest paid player on their roster right now), and Portland didn't want to pay him that much, which is when the Cavs and Nance were brought into the discussion. But Lauri didn't have much time left before he was playing on the Q.O. when that deal was done.
I don't want to overstate it. Signing Lauri to that deal wasn't a fatal mistake. His contract isn't an albatross. It's even conceivable, although unlikely IMO, that he could even play up to that contract. But what I hope fans take away from this is that many a rebuild has been derailed by overpaying role players. Once you're already an over the cap team and your young guys are all extended, it's true cap space matters less. But you can't spend the same dollars twice and every dollar you spend now on multi-year deals is one less available to spend later when opportunities you're not presently aware of present themselves. Further, other teams either like your guys on their contracts when it comes to trading for them, or they don't.