This looks like a trade of Diaz for prospects and Cano for salary relief. They are getting good prospects for Diaz.Can't compare to Chapman trade - that's a July trade for a team looking to win a WS - prices are at a premium. As it is, Ms are getting ascending prospects who haven't rotted on the vine. I certainly wouldn't trade Madrigal and, say, Basabe (an ascending prospect) for Diaz. Diaz had gargantuan K totals and a great one-year WHIP...but high K totals are more and more common; not 15 high but mediocre pitchers are hitting >10Ks/9 these days.
I think the Cano part of the deal is okay for the Mets - they'll get a good 2/3 years out of him and aren't giving up anything. >50% isn't bad; that's about as much as a team can expect if they sign Harper/Machado even at their age.