We only have him for 1.5 seasons, so even if Lamet became a dominant reliever overnight (a huge if), we'd be trading 1.5 seasons of maybe the best reliever in baseball for 2.0 seasons of elite relievers (0.5 of Rogers, 1.5 of Lamet), plus two non-elite prospects.
The only way I'm not disappointed in this trade is if they think Lamet can be a top-of-the-rotation starter again. Burnes-Woodruff-Peralta-Lamet-Lauer/Ashby would be a crazy rotation.