Just wondering, when do you consider a streak (such as Bernadina/Espinosa lately) true talent?

Well, if you want to do it properly, you need to regress it backwards a few years and to league average, giving more weight to recent years, according to the equations we've derived by looking at hundreds of thousands of plate appearances in professional baseball. The hot streaks Bernadina and Espinosa have been on lately (I'm assuming you're talking about BA here?) are definitely

*way* too small a sample size to think there's anything substantial behind them. Morse's last year, on the other hand, is a long enough sample that we know that, at the very least, his power is for real (not that we needed stats to tell us that). The different stats take different amounts of time to stabilize... BA takes around 500 PAs and OBP even more, if I recall correctly.