Reason #3 the Mariners will make the Playoffs: The Staff is Nasty
I saved the best for last. There are so many places you can look around to and find reasons to love this staff. Maybe it's the rankings done by Eno Sarris over at the Athletic (paywall) that have the Mariners as 3 of the best 11 Fantasy SP options, with Miller and Woo at 41/42.
Maybe it's the Cy Young rankings and odds, that have those same top 3 Mariners in the top 8, with Kirby and Castillo both in the top 5.
Or, is it the fact that nearly every single fanbase that is in need of any SP help at all desperately wants their team to make a deal with the Mariners? You can't turn around without getting hit with another article of "Team X should trade for this Mariners starter". Miller and Woo would be #3's on plenty of teams. Gilbert could probably lead some rotations. Kirby and Castillo are both not just #1's, but both Aces. (Yes, there is a difference between a #1 and an Ace)
What's scary is that Kirby, Gilbert, Woo, and Miller are all young and still getting better. I'm not saying that they will all improve on what happened last season, but it's something you can ponder without it being an outlandish possibility to see equal success or stronger seasons from them. If that's the case... woah boy, look out. The Mariners could have the best staff in the league, and it could lead them to not just the playoffs, but the AL West title.