There are a few engine configurations that are inherently balanced and BMW sells a few:
- I6
-V8
-V12 (but not in the GT).
-H4 or 6 'boxer' (not sold by BMW, at least for cars)
While the GT is fairly heavy, I agree, I've never had an issue with the power of the 535 and it is smooth. Few other company's use an I6, and go with a V6, which requires all sorts of things to make it smooth, and then, it never really is as nice as those listed above. The hassle is, though, that it is longer. Fewer cylinders means fewer parts, less internal friction, and the potential for greater efficiency along with less expensive maintenance.