Yup. Getting a batter via the K means you have a 99.99% chance that he will be out. If you rely on more batted ball outs the chances that it isn't an out increase astronomically. Errors, driblers, seeing-eye hits, bloops...all of these mean more baserunners. The best pitchers will almost always be the guys that are really difficult to get the bat on the ball. It is, of course, generally important to not walk tons of guys, too.
Until we get to the time when MLB is filled with 13 guys like that in every roster spot (and we seem to get closer to it every year), teams will have to rely on some pitchers that don't pitch with high k rates.. And yeah, they can be inconsistent because of bad luck, injury, etc. BTW, I always have thought that Burnes has had really bad luck on batted balls. It seemed really weird.
Of course, a lot of these "soft tossers" would rate as above average in velocity even 20 years ago.