Well I think it's not an accurate picture you've painted. Why Scott Laughton?
1. The Habs need a 2C since Dach has not performed as expected as a 2C (so far, anyway)
2. Evans is a pending UFA 3C-at-best who has priced himself out of a renewal (so far, anyway)
3. Cashing in on a pending UFA in a dead-rubber, tank season is generally preferrable when the team's immediate near-future is not clearly competitive*
*Clearly competitive: some expect the Habs to tank or struggle next season, some expect the Habs to be 'in the mix' next season, some expect the Habs to be a playoff team next season. It's all over the place. If an injury to Emil fkn Heineman can derail our forward group, then an untimely injury to Suzuki or Caufield would tank our season next year. So we cannot assume that we will be like MIN, TOR, PIT and survive the loss of our best forward as they did. We're not that deep or skilled.
Evans is in demand at the TDL. If the Habs absolutely want to keep him long-term, they can always circle back as UFA signing season kicks off. Selling him at the TDL to get more assets for trade-or-draft purposes is clearly the right move. Acquiring a 2C is clearly a necessary move, either now or later. Replacing Evans is a third priority, though just as necessary.