Machines are different. My Brother 1500s, straight sewing only, has less top thread showing on the bottom then my other machine. The size of the needle may make a difference, since you state it looks like they are balanced. If the needle is too large for the thread, it makes a larger hole than the thread can fill. With monofilament thread I use a 6.5 microtex to get a very small hole even on a quilting sandwich. Both of my machines are 15yr+ old and don't have a "balance adjusting thingy".
As to "eyelashes" at sharp turns, taking 2-3 stitches verying close together will minimize that.