Its obviously not fair to call Sanchez an elite reliever right now. The results have been good, but the underlying numbers are not to that standard.
On the other hand, I don't think its fair to call him some sort of bust already. Reasonable people take FIP stats as the best way to evaluate how well a pitcher has actually performed. Its not really an interesting discussion anymore, its been shown to be true. I think the more interesting argument is which pitchers can outperform their FIP in the long term, and why that is. 100% not saying I believe Sanchez will do this, but its interesting to think about.