It's common for the Twins to cite a prospect's lack of "consistency" in the minors as an excuse for why they haven't been called up. Most recently they did so with Triple-A reliever Lester Oliveros, who has a 1.65 ERA and 109 strikeouts in 76 innings since last season. Sustained dominance like that makes the notion of Oliveros lacking "consistency" seem absurd, particularly compared to the low standards for "consistency" the Twins so often seem to have for mediocre veterans.
Another problem with the Twins citing a lack of "consistency" whenever it suits them is that when it doesn't suit them they're quick to ignore the concept.