Not only do you not really seem to understand that certain stats can have meaning within less sample than others, you also don't seem to follow the notion that no one f***ing knows what Sanchez is going to be, but that doesn't stop us from making an educated guess by using the best knowledge we have, what we can discern from his brief MLB stint (GB%: very good (I think I forget off the top of my head), SwStr: Extremely concerning), his MiLB numbers (horrendous), and the eye test (very good). So, we've got two very good things, the eye test and the GB rate. Problem is, it's unlikely that those two outweigh the SwStr, which is very very very bad in MLB, and pretty meh in MiLB, which is a very important measure, and the rest of his MiLB numbers.
TLDR No, we don't know what he'll be, but that isn't any sort of justification for him playing. What we can guess, based off of what has already happened, is that he will not be very good. He could be very good, but our educated guess would be otherwise.
Now, I'm going to stop before my jimmies reach full rustle.
@oracle gif me missing the forest for the trees