Rob Johnson appears to be the choice to take Josh Thole's spot on the roster, hopefully only temporarily. Most or the analysis of Johnson I've seen suggests that he's woefully inadequate even as a backup. Although I tend to largely agree with that analysis, I figured it couldn't hurt to play devil's advocate.
Looking primarily at Johnson's minor league stats, what jumped out at me is that he seemed to have been rushed through the Mariners' system. The median ages for low-A, high-A, AA, and AAA are 22, 23, 24, and 26 respectively. Johnson went from Rookie to High-A ball in the span of 2 seasons when he was 20 and 21. As a 21-year-old, he actually acquitted himself decently as a hitter, OPS-ing .764 between A and high-A. But only 86 of his plate appearances were in the high-A environment of the California League. The vast majority were in the Class A Midwest League - the equivalent of the Sally League, where Savannah plays.
Then, at 22, Johnson was asked to make the jump from high-A to AAA, despite having only 86 plate appearancees in high-A ball and none at AA. In retrospect, this was a huge mistake. Johnson predictably struggled mightily to the tune of a woeful .578 OPS over 359 plate appearances. Yes, given that this was the PCL that's even worse than it sounds, but I think it was excusable given the enormous jump he was being asked to make in terms of talent level. That said, Johnson improved in each of his next 2 years and OPS'd .804 in Tacoma as a 24-year-old.
As a major leaguer, we know the deal - he's been an awful hitter. And at some point, that's indicative of how he'd perform now. But he's been an adequate hitter at AAA in each of his seasons there other than the aforementioned first season, including this year, where he's OPS-ing over .800 in limited duty at Buffalo. Does that mean that he's going to be fantastic? No. But I think he may be a bit better than we're giving him credit for, and given that he was rushed through the Mariners' system without the benefit of getting ABs at each level, that might account for his slow development as a hitter. At the very least, he might be better than he's shown so far in the majors.