Ryan Sloan’s season line looks like the kind of thing that makes Mariners fans start wondering if something is wrong. A 5.65 ERA and 1.60 WHIP through four starts at Double-A Arkansas is not exactly the cleanest way to announce yourself as one of the fastest-rising arms in baseball. But this is where we have to be careful. Not every ugly ERA is built the same way. Sloan’s start has been shaky, but it has also been a little deceiving. The Mariners’ 20-year-old right-hander hasn’t suddenly stopped missing bats. That’s the first thing that matters. Even with the early turbulence, Sloan has struck out 17 hitters in 14 1/3 innings for Arkansas, and MiLB’s own highlight from his latest outing against Corpus Christi showed him punching out seven over 4 2/3 innings. That was his best start of the young season, and it came with the kind of finish that makes the surface panic feel a little premature.   Ryan Sloan threw it very well today. One mistake on a 2-run HR.…