The Mariners have had the best offseason so far and you might disagree but hear me out. They lost Teoscar Hernandez, an average bat, below average defender and a guy that has declined every year for the last 3 years. They lost Eugenio Suarez, an older player who showed some serious signs of regression (significantly slower bat speed) and regressed to be about an average bat.
You added Luis Urias who was a 2.5-win player and a 110 wRC+ or better for back-to-back seasons. He controls the zone very well, doesn't strike out and could very well replicate Geno's production. You also added Mitch Garver, a career 123 wRC+, with really solid walk and strikeout rates. Garver put up a 2.1 fWAR last year in only 87 games. With the Mariners planning to strictly play him at DH if he can play 120-130 games, he could more than make up the production you lost.
The Astros haven't added much but lost two solid bullpen arms. The Angels lost the best player in the world while adding an injured first baseman and not much else. The Rangers may have had the worst offseason after losing one of their best starting pitchers to free agency, another one for half the year to injury and one of their best bats to the Mariners.