Alvarado is a beast from the left side, there's no worries there if he stays healthy, although teams usually like closers to be from the right side. Castillo can just get a bit wild.So, the Rays got a wake up call by the Red Sox over the weekend, that's for sure.
Of course, slumps are part of baseball, and keeping a .700 average across a season is unsustainable. It was an interesting four game slump, though: Against Baltimore, the Rays were behind but scored a tying run in the 9th, losing by one in the 11th; in the second game against Boston, the Rays were behind but scored the tying run in the 8th, losing by one in the 9th; in the third game against Boston, the Rays were behind AGAIN but scored the tying run AGAIN in the 9th, losing AGAIN in the 11th. So they have been able to get back from behind, but not bump ahead.
Also, I'm reminded of something MadTigerFan noted with Seattle - that eventually batters would figure out the Mariners' pitchers. I think his point also counts for Tampa Bay's closers: Castillo and Alverado had been suffocating for the first month, but it seemed like they lost some of their mystery against Boston.
Just like the Athletics with Trivino and Treinen the Devil Rays are using their 2 main relievers too much though, other guys need to step up or they'll be out of gas by June/July.