Hilariously ironic that everyone who thinks Sanchez will bust wants to trade him for Jeff Samardzija.
Shark had a 1.63 K/BB in the minor leagues, over almost 500 innings. Just a 6.3 K/9, and a fairly bad 3.9 BB/9.
In a nutshell, I'd take Sanchez' minor league peripherals (1.87 K/BB, 9.0 K/9, and 4.8 BB/9) over Samardzija's. At least Sanchez is demonstrating the ability to miss a decent amount of bats, along with limiting runs (take it as a poor proxy measurement of inducing weak contact) and getting ground balls (56.3% according to MLB. Shark's minor league GB% not readily available but his major league mark is a pedestrian 45.4%.). [No, I'm not saying that trading Sanchez for Samardzija would be dumb.]
Some people get way too caught up in Sanchez' K and BB rates. He's probably simultaneously overrated by scouts and underrated by SABR minded stat-line "scouts". In my view, guys with great s*** who don't K/BB very well in the minors like Sanchez, Chris Archer, Zack Wheeler, and Archie Bradley aren't significantly different from guys like Syndergaard and Stroman that do. They'll all get to the big leagues, probably run into bumps in the road, and have to make adjustments. Over 60% of highly regarded pitching prospects disappoint. It's a crapshoot. Names out of a hat, practically. Development is not linear and peripherals don't translate to the big leagues in a linear fashion. Some guys with good minor league peripherals struggle to post great K and BB rates in the big leagues (ex., Danny Duffy, Hellickson, Matt Moore, Dan Straily). Others do the opposite, although it's certainly much more rare (Samardzija, Lance Lynn?, Josh Johnson, ROY HALLADAY).